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Gruetzner, J, Espejo FJJ, Lathika N, Uenzelmann-Neben G, Hall IR, Hemming SR, LeVay LJ, Barker S, Berke MA, Brentegani L, Caley T, Cartagena-Sierra A, Charles CD, Coenen JJ, Crespin JG, Franzese AM, Han X, Hines SKV, Just J, Koutsodendris A, Kubota K, Norris RD, Santos TP, Robinson R, Rolinson JM, Simon MH, Tangunan D, van der Lubbe HJL, Yamane M, Zhang H, Expedition S.  2019.  A new seismic stratigraphy in the Indian-Atlantic Ocean gateway resembles major paleo-oceanographic changes of the last 7 Ma. Geochemistry Geophysics Geosystems. 20:339-358.   10.1029/2018gc007668   AbstractWebsite

The exchange of water masses between the Indian Ocean and the Atlantic constitutes an integral interocean link in the global thermohaline circulation. Long-term changes in deep water flow have been studied using seismic reflection profiles but the seismic stratigraphy was poorly constrained and not resolved for the time period from the late Miocene onward. Here we present results from International Ocean Discovery Program Site U1475 (Agulhas Plateau) located over a sediment drift proximal to the entrance of North Atlantic Deep Water into the Southern Ocean and South Indian Ocean. Site U1475 comprises a complete carbonate-rich stratigraphic section of the last similar to 7 Ma that provides an archive of climate-induced variations in ocean circulation. Six marker reflectors occurring in the upper 300 m of the drift are identified here for the first time. The formation of these reflectors is mainly due to density changes that are mostly caused by changes in biogenic versus terrigenous sediment deposition. Synthetic seismograms allow age assignments for the horizons based on biostratigraphy and magnetostratigraphy. Prominent reflectors are related to late Pleistocene glacial/interglacial variability, the middle and early Pleistocene transitions, and the onset of the northern hemisphere glaciation. A peculiar early Pliocene interval (similar to 5.3-4.0 Ma) bounded by two reflectors is characterized by fourfold elevated sedimentation rates (> 10 cm/kyr) and the occurrence of sediment waves. We argue that this enhanced sediment transport to the Agulhas Plateau was caused by a reorganization of the bottom current circulation pattern due to maximized inflow of North Atlantic Deep Water.

Sibert, E, Friedman M, Hull P, Hunt G, Norris R.  2018.  Two pulses of morphological diversification in Pacific pelagic fishes following the Cretaceous - Palaeogene mass extinction. Proceedings of the Royal Society B-Biological Sciences. 285   10.1098/rspb.2018.1194   AbstractWebsite

Molecular phylogenies suggest some major radiations of open-ocean fish clades occurred roughly coincident with the Cretaceous-Palaeogene (K/Pg) boundary, however the timing and nature of this diversification is poorly constrained. Here, we investigate evolutionary patterns in ray-finned fishes across the K/Pg mass extinction 66 million years ago (Ma), using microfossils (isolated teeth) preserved in a South Pacific sediment core spanning 72-43 Ma. Our record does not show significant turnover of fish tooth morphotypes at the K/Pg boundary: only two of 48 Cretaceous tooth morphotypes disappear at the event in the South Pacific, a rate no different from background extinction. Capture-mark-recapture analysis finds two pulses of origination in fish tooth morphotypes following the mass extinction. The first pulse, at approximately 64 Ma, included short-lived teeth, as well as forms that contribute to an expansion into novel morpho-space. A second pulse, centred at approximately 58 Ma, produced morphotype novelty in a different region of morphospace from the first pulse, and contributed significantly to Eocene tooth morphospace occupation. There was no significant increase in origination rates or expansion into novel morphospace during the early or middle Eocene, despite a near 10-fold increase in tooth abundance during that interval. Our results suggest that while the K/Pg event had a minor impact on fish diversity in terms of extinction, the removal of the few dominant Cretaceous morphotypes triggered a sequence of origination events allowing fishes to rapidly diversify morphologically, setting the stage for exceptional levels of ray-finned fish diversity in the Cenozoic.

Tangunan, DN, Baumann KH, Just J, LeVay LJ, Barker S, Brentegani L, De Vleeschouwer D, Hall IR, Hemming S, Norris R, Expedition 361 Shipboard Sci P.  2018.  The last 1 million years of the extinct genus Discoaster: Plio-Pleistocene environment and productivity at Site U1476 (Mozambique Channel). Palaeogeography Palaeoclimatology Palaeoecology. 505:187-197.   10.1016/j.palaeo.2018.05.043   AbstractWebsite

A detailed paleoenvironment reconstruction from the Mozambique Channel, western Indian Ocean, based on the calcareous nannoplankton assemblages was conducted for the interval between 2.85 and 1.85 Myr. This study covers the period during which the successive extinction of the last five species of discoasters occurred. New productivity data obtained from the abundances of the Discoaster species (Discoaster brouweri, D. triradiatus, D. pentaradiatus, D surculus, and D. tamalis) and other indicative calcareous nannoplankton taxa showed abundance variations, which were at paced with the 100, 41, and 23 kyr astronomical periodicities. A shift in the productivity and water-column stratification proxies occurred at similar to 2.4 Ma, after the onset of the Northern Hemisphere glaciation. Here we propose that the variability recorded at International Ocean Discovery Program Site U1476 reflects the interplay between forcing associated with warm tropical Pacific and cold southern ocean influences. The former is shown by consistent occurrence of warm water taxa (Calcidiscus leptoporus, Oolithotus spp., Rhabdosphaera clavigera, Syracosphaera spp., Umbellosphaera spp.), typical of Indonesian Throughflow surface waters. On the other hand, the occurrence of Coccolithus pelagicus indicates the influence of cold, nutrient-rich sub-Antarctic surface waters. A more mixed water column initiated at similar to 2.4 Ma, and a consequent productivity increase led to the gradual reduction of the Discoaster species, until their extinction at 1.91 Ma. This period was characterized by the low values of the Florisphaera profunda index and high abundances of upper photic zone flora, indicative of nutrient-rich surface water conditions. High productivity at the location during this period could have also been amplified by localized upwelling events driven by the Mozambique Channel eddies.

Lukowiak, M, Cramer KL, Madzia D, Hynes MG, Norris RD, O'Dea A.  2018.  Historical change in a Caribbean reef sponge community and long-term loss of sponge predators. Marine Ecology Progress Series. 601:127-137.   10.3354/meps12694   AbstractWebsite

Sponges are an ecologically important component of modern Caribbean coral reefs. However, little is known about the structure of sponge communities prior to the large-scale degradation of Caribbean reef ecosystems. Here we explore changes in the sponge community over the past millennium by analyzing the composition of sponge spicules from a sediment core collected from a lagoonal reef within the archipelago of Bocas del Toro, Caribbean Panama. The analysis reveals a change in spicule composition that began approximately 400 yr ago. During this time, the share of monaxial spicules, belonging mostly to haplosclerid and axinellid sponges, decreased while the relative number of spherical spicules, found typically in Placospongia, Geodia, and some chondrillids, increased. These results were compared with previously published data on parrotfish, corals, and reef accretion rates obtained from the same core. The increased share of spherical spicules did not correlate with contemporaneous declines in the abundance of parrotfish (de termined from fish teeth) or with trends in the relative abundance of dominant coral species (determined from coral skeletal remains) but was weakly correlated with reef accretion rates (de termined from sediment accumulation rates). Spicule morphogroup diversity and evenness increased over the past similar to 400 yr, suggesting community changes were not due to reef environments becoming less habitable for reef sponges. Although not tested directly, the increase in spherical spicules may be due to declines in the abundance of sea turtles that preferentially feed on sponges that contain these spicule types.

Friedrich, O, Bornemann A, Norris RD, Erbacher J, Fiebig J.  2018.  Changes in tropical Atlantic surface-water environments inferred from late Albian planktic foraminiferal assemblages (ODP Site 1258, Demerara Rise). Cretaceous Research. 87:74-83.   10.1016/j.cretres.2017.05.028   AbstractWebsite

Abundance patterns of planktic and benthic foraminifera from the middle to upper Albian of tropical Atlantic Ocean Drilling Program Site 1258 (Demerara Rise) display a pronounced shift between two clearly distinguishable assemblages: (1) a foraminiferal fauna dominated by coiled taxa, which is inferred to represent a deep and/or weak oxygen minimum zone, and (2) abundant clavate and biserial taxa, inferred to record a shallow and/or strong oxygen minimum zone at Demerara Rise. The entire sequence is rich in organic matter (3-6 wt% TOC) of a marine phytoplankton origin (delta C-13 similar to -28 parts per thousand), consistent with a highly productive region. Both the high productivity and changes in foraminiferal assemblages are consistent with changes in the mean latitudinal position of the Intertropical Convergence Zone (ITCZ) over the South American continent. Movements of the ITCZ are proposed to reduce the amount of runoff during the 'clavate-dominated' cycles, leading to the intensification of upwelling and therefore a stronger oxygen minimum zone compared to the intervals dominated by coiled foraminifera. We have previously found a similar hydrographic cycle in Turonian to Coniacian sections from the same area suggesting that this climate cyclicity and palaeogeography was long-lived off NE South America (similar to 15 million years). Due to the stratigraphic position of the interval with high abundances of clavate planktic foraminifera and the inferred strong oxygen minimum zone, it is tentatively proposed that this interval represents a local expression of the OAE 1c event within the long-living Demerara Rise upwelling system. (C) 2017 Elsevier Ltd. All rights reserved.

Batenburg, SJ, Friedrich O, Moriya K, Voigt S, Cournede C, Moebius I, Blum P, Bornemann A, Fiebig J, Hasegawa T, Hull PM, Norris RD, Rohl U, Sexton PF, Westerhold T, Wilson PA, Scientists IE342.  2018.  Late Maastrichtian carbon isotope stratigraphy and cyclostratigraphy of the Newfoundland Margin (Site U1403, IODP Leg 342). Newsletters on Stratigraphy. 51:245-260.   10.1127/nos/2017/0398   AbstractWebsite

Earth's climate during the Maastrichtian (latest Cretaceous) was punctuated by brief warming and cooling episodes, accompanied by perturbations of the global carbon cycle. Superimposed on a long-term cooling trend, the middle Maastrichtian is characterized by deep-sea warming and relatively high values of stable carbon-isotope ratios, followed by strong climatic variability towards the end of the Cretaceous. A lack of knowledge on the timing of climatic change inhibits our understanding of underlying causal mechanisms. We present an integrated stratigraphy from Integrated Ocean Drilling Program (IODP) Site U1403, providing an expanded deep ocean record from the North Atlantic (Expedition 342, Newfoundland Margin). Distinct sedimentary cyclicity suggests that orbital forcing played a major role in depositional processes, which is confirmed by statistical analyses of high resolution elemental data obtained by X-ray fluorescence (XRF) core scanning. Astronomical calibration reveals that the investigated interval encompasses seven 405-kyr cycles (Ma(405)1 to Ma(405)7) and spans the 2.8 Myr directly preceding the Cretaceous/Paleocene (K/Pg) boundary. A high-resolution carbon-isotope record from bulk carbonates allows us to identify global trends in the late Maastrichtian carbon cycle. Low-amplitude variations (up to 0.4%) in carbon isotopes at Site U1403 match similar scale variability in records from Tethyan and Pacific open-ocean sites. Comparison between Site U1403 and the hemipelagic restricted basin of the Zumaia section (northern Spain), with its own well-established independent cyclostratigraphic framework, is more complex. Whereas the pre-K/Pg oscillations and the negative values of the Mid-Maastrichtian Event (MME) can be readily discerned in both the Zumaia and U1403 records, patterns diverge during a similar to 1 Myr period in the late Maastrichtian (67.8-66.8 Ma), with Site U1403 more reliably reflecting global carbon cycling. Our new carbon isotope record and cyclostratigraphy offer promise for Site U1403 to serve as a future reference section for high-resolution studies of late Maastrichtian paleoclimatic change.

Egger, LM, Bahr A, Friedrich O, Wilson PA, Norris RD, van Peer TE, Lippert PC, Liebrand D, Pross J.  2018.  Sea-level and surface-water change in the western North Atlantic across the Oligocene-Miocene Transition: A palynological perspective from IODP Site U1406 (Newfoundland margin). Marine Micropaleontology. 139:57-71.   10.1016/j.marmicro.2017.11.003   AbstractWebsite

The Oligocene-Miocene transition (OMT; similar to 23.1 Ma) terminates the late Oligocene warming trend and is marked by a transient, large-amplitude expansion of Antarctic ice sheets. The associated glacial maximum, which is expressed by a similar to 1 positive shift in benthic foraminiferal oxygen-isotope values, is commonly referred to as the 'Mi-1 isotope event'. Whereas the causes for the glacial maximum at the OMT are intrinsically connected to Southern Hemisphere ice-sheet dynamics, the behavior of the surface ocean in the Northern Hemisphere during this time is poorly known. To contribute to a better understanding of the paleoceanographic evolution during the OMT in the higher-latitude North Atlantic, we have analysed both marine and terrestrial palynomorphs from Integrated Ocean Drilling Program (IODP) Site U1406 offshore Newfoundland; this site has yielded a complete OMT section and exhibits a high-quality magnetostratigraphy that provides precise age control and allows reliable correlation to other records beyond Newfoundland. Our palynological data, which span the interval from 23.3 to 22.5 Ma and have a mean temporal resolution of 11.9 kyrs, show strong similar to 110-kyr eccentricity-paced oscillations during the earliest Miocene; these oscillations are in phase with similar cyclicity identified in previously published benthic foraminiferal oxygen-isotope records. More specifically, a pronounced sea-level variability is documented by the abundances of neritic dinoflagellate cysts (dinocysts) and terrigenous palynomorphs, which both reach maxima during peak glacial intervals as inferred from previously published South Atlantic benthic oxygen-isotope data. A decline in the abundance of warmer-water dinocysts suggests a surface-water cooling offshore Newfoundland from the latest Oligocene onwards. Surface-water productivity (as derived from the ratio between heterotrophic and autotrophic dinocysts) remained generally low throughout the studied interval. Notably, this ratio does not exhibit any correlation with changes in surface-water temperature, which is estimated from the ratio of warm-water over cold-water dinocysts. Together with the consistently low surface-water productivity, the lack of a correlation between surface-water productivity and temperature makes it highly unlikely that the observed paleoceanographic change was caused by a southward migration of the Arctic Front. Instead, we argue that our data may document an enhanced influence of the (Proto-) Labrador Current on surface waters offshore Newfoundland during the earliest Miocene that suppressed the influence of the Gulf Stream in this region of the Northwest Atlantic. We speculate that the enhanced influence of the (Proto-) Labrador Current was triggered by cooling of the northern hemisphere and possibly modulated by high-latitude sea-ice expansion.

Sibert, EC, Cramer KL, Hastings PA, Norris RD.  2017.  Methods for isolation and quantification of microfossil fish teeth and elasmobranch dermal denticles (ichthyoliths) from marine sediments. Palaeontologia Electronica. 20:1-14. Abstract

Ichthyoliths — microfossil fish teeth and shark dermal scales (denticles) — are found in nearly all marine sediments. Their small size and relative rarity compared to other microfossil groups means that they have been largely ignored by the paleontology and paleoceanography communities, except as carriers of certain isotopic systems. Yet, when properly concentrated, ichthyoliths are sufficiently abundant to reveal patterns of fish abundance and diversity at unprecedented temporal and spatial resolution, in contrast to the typical millions of years-long gaps in the vertebrate body fossil record. In addition, ichthyoliths are highly resistant to dissolution, making it possible to reconstruct whole fish communities over highly precise and virtually continuous timescales. Here we present methods to isolate and utilize ichthyoliths preserved in the sedimentary record to track fish community structure and ecosystem productivity through geological and historical time periods. These include techniques for isolation and concentration of these microfossils from a wide range of sediments, including deep-sea and coral reef carbonates, clays, shales, and silicate-rich sediments. We also present a novel protocol for ichthyolith staining using Alizarin Red S to easily visualize and distinguish small teeth from debris in the sample. Finally, we discuss several metrics for quantification of ichthyolith community structure and abundance, and their applications to reconstruction of ancient marine food webs and environments.

Cramer, KL, O'Dea A, Carpenter C, Norris RD.  2017.  A 3,000 year record of Caribbean reef urchin communities reveals causes and consequences of long-term decline in Diadema antillarum. Ecography. : Blackwell Publishing Ltd   10.1111/ecog.02513   Abstract

Urchins are the last abundant grazers of macroalgae on most Caribbean reefs following the historical overexploitation of herbivorous fishes. The long-spined urchin Diadema antillarum was particularly effective at controlling macroalgae and facilitating coral dominance on Caribbean reefs until its ecological extinction from a catastrophic disease epidemic in the early 1980s. Despite their important role in the structure and functioning of Caribbean reef ecosystems, the natural dynamics of Caribbean reef urchin communities are poorly known due to the paucity of ecological survey data prior to large-scale human disturbances and the Diadema dieoff. To help resolve the baseline abundances and ecological roles of common urchin taxa, we track changes in urchin abundance and composition over the past 3,000 years from analysis of subfossil urchin spines preserved in reef matrix cores collected in Caribbean Panama. Echinometra consistently dominated the subfossil spine assemblage, while Diadema was consistently rare in the subfossil record in this region. Rather than increasing during a period of heightened human exploitation of their fish competitors and predators, Diadema began declining over a millennium ago. Convergent cross mapping (CCM) causality analyses reveal that Diadema abundance is causally related to coral community composition. Diadema is negatively affected by Acropora cervicornis dominance, likely due to the tight association between this coral and the threespot damselfish, an effective Diadema competitor. Conversely, Diadema positively affects the abundance of the coral Madracis mirabilis, possibly via its control of macroalgae. Causal relationships were not detected among abundances of individual urchin taxa, indicating that inter-specific echinoid competition is not a factor limiting Diadema recovery. Our detailed record of prehistorical and historical urchin community dynamics suggests that the failure of Diadema to recover over 30 years after its mass mortality event may be due in part to the prey release of damselfish following the long-term overfishing of piscivorous fishes. This article is protected by copyright. All rights reserved.

Boyle, PR, Romans BW, Tucholke BE, Norris RD, Swift SA, Sexton PF.  2017.  Cenozoic North Atlantic deep circulation history recorded in contourite drifts, offshore Newfoundland, Canada. Marine Geology. 385:185-203.   10.1016/j.margeo.2016.12.014   AbstractWebsite

In the North Atlantic Ocean, contour-following deep currents have created regional erosional unconformities and deposited contourite drifts that exceed 2 km in thickness and extend for 100 s of km. The stratigraphic records in the drifts have been used to reconstruct variations in North Atlantic deep-water circulation throughout the Cenozoic; however, uncertainties remain about certain aspects of the timing, intensity, depth distribution, and regional impact of these currents. Here, we use an integrated dataset of seismic-reflection profiles and IODP core data (lithology, biostratigraphy, and magnetostratigraphy) to document sedimentation history and the development of current effects in the Cretaceous to present sedimentary record on the J-Anomaly Ridge and Southeast Newfoundland Ridge, offshore Newfoundland, Canada. The Newfoundland ridges are in a key location, lying between well-studied areas in the northern and western North Atlantic and under the path of both the modern Deep Western Boundary Current and the Gulf Stream. Late Cretaceous through Early Eocene sedimentation on the ridges was dominated by biogenic pelagic sedimentation, but at similar to 47 Ma, near the Early-Middle Eocene boundary, well developed contourite drifts began to accrete in paleo-water depths of similar to 4000-4500 m, accompanied by an order-of-magnitude increase in terrigenous sediment mass accumulation rates. From this time forward, drift deposition, interrupted by brief episodes of erosion, continued unabated. This timing for the onset of persistent deep currents is coincident with reorganization of Atlantic circulation inferred from a change from biosiliceous to non-biosiliceous sedimentation in the western North Atlantic (Horizon A(C)) and with the current-eroded Intra-Eocene Unconformity (IEU) in the northern North Atlantic A change in sedimentation style occurred within the Middle Eocene to upper Oligocene drift sequence, and it likely was related to a shift to deeper, more intense currents that eroded the widespread Horizon A(U) along the margin of eastern North America about Early Oligocene time. Beginning in the Late Oligocene (similar to 25 Ma) a thick drift exhibiting seismically laminated mudwaves was deposited in a distinct belt at similar to 3500-4500 m paleodepth on the Southeast Newfoundland Ridge. This development correlates with widespread Late Oligocene through Miocene-Pliocene drift accumulation throughout the North Atlantic. The most recent phase of drift deposition, since Late Pliocene time (similar to 3 Ma), occurred after a shift to the 'modern' circulation system of deeper, swifter currents, and it includes mixed pelagic-hemipelagic sediments and ice-rafted debris that reflect glacial-interglacial influences on sedimentation. (C) 2017 Elsevier B.V. All rights reserved.

Dillon, EM, Norris RD, O'Dea A.  2017.  Dermal denticles as a tool to reconstruct shark communities. Marine Ecology Progress Series. 566:117-134.   10.3354/meps12018   AbstractWebsite

The last 50 yr of fisheries catch statistics and ecological surveys have reported significant decreases in shark populations, which have largely been attributed to human activities. However, sharks are challenging to census, and this decline likely pre-dated even the longest fishery- dependent time series. Here we present the first use of dermal denticles preserved in reef sediments as a novel tool to reconstruct shark communities. We first built a dermal denticle reference collection and conducted a morphometric analysis of denticle characters to relate denticle form to taxonomy, shark ecology, and denticle function. Denticle morphology was highly variable across the body of an individual shark and between taxa, preventing species-or genus-level identification of isolated denticles. However, we found that denticle morphology was strongly correlated with shark ecology, and morphometric analysis corroborated existing functional classifications. In a proof of concept, we extracted 330 denticles from modern and fossil reef sediments in Bocas del Toro, Panama and found them to be morphologically diverse and sufficiently well-preserved to allow classification. We observed a high degree of correspondence between the denticles found in the sediments and the sharks documented in the region. We therefore propose that (1) denticle assemblages in the recent fossil record can help establish quantitative pre-human shark baselines and (2) time-averaged denticle assemblages on modern reefs can supplement traditional surveys, which may prove especially valuable in areas where rigorous surveys of sharks are difficult to perform.

Cramer, KL, O’Dea A, Clark TR, Zhao J-xin, Norris RD.  2017.  Prehistorical and historical declines in Caribbean coral reef accretion rates driven by loss of parrotfish. Nature Communications. 8:14160.: The Author(s)   10.1038/ncomms14160   Abstract

Caribbean coral reefs have transformed into algal-dominated habitats over recent decades, but the mechanisms of change are unresolved due to a lack of quantitative ecological data before large-scale human impacts. To understand the role of reduced herbivory in recent coral declines, we produce a high-resolution 3,000 year record of reef accretion rate and herbivore (parrotfish and urchin) abundance from the analysis of sediments and fish, coral and urchin subfossils within cores from Caribbean Panama. At each site, declines in accretion rates and parrotfish abundance were initiated in the prehistorical or historical period. Statistical tests of direct cause and effect relationships using convergent cross mapping reveal that accretion rates are driven by parrotfish abundance (but not vice versa) but are not affected by total urchin abundance. These results confirm the critical role of parrotfish in maintaining coral-dominated reef habitat and the urgent need for restoration of parrotfish populations to enable reef persistence.

Egger, LM, Sliwinska KK, van Peer TE, Liebrand D, Lippert PC, Friedrich O, Wilson PA, Norris RD, Pross J.  2016.  Magnetostratigraphically-calibrated dinoflagellate cyst bioevents for the uppermost Eocene to lowermost Miocene of the western North Atlantic (IODP Expedition 342, Paleogene Newfoundland sediment drifts). Review of Palaeobotany and Palynology. 234:159-185.   10.1016/j.revpalbo.2016.08.002   AbstractWebsite

The Oligocene epoch represents a somewhat neglected chapter in paleoclimate and paleoceanographic history, which is at least partially due to the scarcity of complete Oligocene sedimentary archives and poor biostratigraphic age control. Many of the biotic events registered in Oligocene microfossils are strongly diachronous across latitudes as a response to increased global cooling and enhanced meridional temperature gradients. To improve biostratigraphic age control for the Oligocene of the North Atlantic Ocean, we carried out a high-resolution study of dinoflagellate cysts from Integrated Ocean Drilling Program (IODP) Sites U1405, U1406 and U1411 off Newfoundland. Together the sites comprise an apparently complete uppermost Eocene (34.9 Ma) to lowermost Miocene (21.7 Ma) sequence with good magnetostratigraphic age control. This allows us to firmly tie identified dinoflagellate cyst bioevents to the geomagnetic polarity timescale. In the dinoflagellate cyst assemblages studied we have identified and magnetostratigraphically-calibrated ten first and 19 last appearance datums. Our magnetostratigraphically-calibrated dinocyst-based biostratigraphy, which is based on an average sample resolution of a sample every similar to 150 kyrs, will contribute to an improved age framework for future paleoceanographical studies in the higher-latitude North Atlantic. (C) 2016 Elsevier B.V. All rights reserved.

Bornemann, A, D'Haenens S, Norris RD, Speijer RP.  2016.  The demise of the early Eocene greenhouse - Decoupled deep and surface water cooling in the eastern North Atlantic. Global and Planetary Change. 145:130-140.   10.1016/j.gloplacha.2016.08.010   AbstractWebsite

Early Paleogene greenhouse climate culminated during the early Eocene Climatic Optimum (EECO, 50 to 53 Ma). This episode of global warmth is subsequently followed by an almost 20 million year-long cooling trend leading to the Eocene-Oligocene glaciation of Antarctica. Here we present the first detailed planktic and benthic foraminiferal isotope single site record (delta C-13, delta O-18) of late Paleocene to middle Eocene age from the North Atlantic (Deep Sea Drilling Project Site 401, Bay of Biscay). Good core recovery in combination with well preserved foraminifera makes this site suitable for correlations and comparison with previously published long-term records from the Pacific Ocean (e.g. Allison Guyot, Shatsky Rise), the Southern Ocean (Maud Rise) and the equatorial Atlantic (Demerara Rise). Whereas our North Atlantic benthic foraminiferal delta O-18 and delta C-13 data agree with the global trend showing the long-term shift toward heavier delta O-18 values, we only observe minor surface water delta O-18 changes during the middle Eocene (if at all) in planktic foraminiferal data. Apparently, the surface North Atlantic did not cool substantially during the middle Eocene. Thus, the North Atlantic appears to have had a different surface ocean cooling history during the middle Eocene than the southern hemisphere, whereas cooler deep-water masses were comparatively well mixed. Our results are in agreement with previously published findings from Tanzania, which also support the idea of a muted post-EECO surface-water cooling outside the southern high-latitudes. (C) 2016 Elsevier B.V. All rights reserved.

Penman, DE, Turner SK, Sexton PF, Norris RD, Dickson AJ, Boulila S, Ridgwell A, Zeebe RE, Zachos JC, Cameron A, Westerhold T, Rohl U.  2016.  An abyssal carbonate compensation depth overshoot in the aftermath of the Palaeocene-Eocene Thermal Maximum. Nature Geoscience. 9:575-+.   10.1038/ngeo2757   AbstractWebsite

During the Palaeocene-Eocene Thermal Maximum (PETM) about 56 million years ago, thousands of petagrams of carbon were released into the atmosphere and ocean in just a few thousand years, followed by gradual sequestration over approximately 200,000 years. If silicate weathering is one of the key negative feedbacks that removed this carbon, a period of seawater calcium carbonate saturation greater than pre-event levels would be expected during the event's recovery phase. In marine sediments, this should be recorded as a temporary deepening of the depth below which no calcite is preserved - the calcite compensation depth (CCD). Previous and new sedimentary records from sites that were above the pre-PETM CCD show enhanced carbonate accumulation following the PETM. A new record from an abyssal site in the North Atlantic that lay below the pre-PETM CCD shows a period of carbonate preservation beginning about 70,000 years after the onset of the PETM, providing the first direct evidence for an over-deepening of the CCD. This record confirms an overshoot in ocean carbonate saturation during the PETM recovery. Simulations with two earth system models support scenarios for the PETM that involve a large initial carbon release followed by prolonged low-level emissions, consistent with the timing of CCD deepening in our record. Our findings indicate that sequestration of these carbon emissions was most likely the result of both globally enhanced calcite burial above the CCD and, at least in the North Atlantic, an over-deepening of the CCD.

Sibert, E, Norris R, Cuevas J, Graves L.  2016.  Eighty-five million years of Pacific Ocean gyre ecosystem structure: long-term stability marked by punctuated change. Proceedings of the Royal Society B-Biological Sciences. 283   10.1098/rspb.2016.0189   AbstractWebsite

While the history of taxonomic diversification in open ocean lineages of ray-finned fish and elasmobranchs is increasingly known, the evolution of their roles within the open ocean ecosystem remains poorly understood. To assess the relative importance of these groups through time, we measured the accumulation rate of microfossil fish teeth and elasmobranch dermal denticles (ichthyoliths) in deep-sea sediment cores from the North and South Pacific gyres over the past 85 million years (Myr). We find three distinct and stable open ocean ecosystem structures, each defined by the relative and absolute abundance of elasmobranch and ray-finned fish remains. The Cretaceous Ocean (pre-66 Ma) was characterized by abundant elasmobranch denticles, but lowabundances of fish teeth. The Palaeogene Ocean (66-20 Ma), initiated by the Cretaceous/Palaeogene mass extinction, had nearly four times the abundance of fish teeth compared with elasmobranch denticles. This Palaeogene Ocean structure remained stable during the Eocene greenhouse (50 Ma) and the Eocene-Oligocene glaciation (34 Ma), despite large changes in the overall accumulation of both groups during those intervals, suggesting that climate change is not a primary driver of ecosystem structure. Dermal denticles virtually disappeared from open ocean ichthyolith assemblages approximately 20 Ma, while fish tooth accumulation increased dramatically in variability, marking the beginning of the Modern Ocean. Together, these results suggest that open ocean fish community structure is stable on long timescales, independent of total production and climate change. The timing of the abrupt transitions between these states suggests that the transitions may be due to interactions with other, non-preserved pelagic consumer groups.

Sibert, EC, Norris RD.  2015.  New Age of Fishes initiated by the Cretaceous−Paleogene mass extinction. Proceedings of the National Academy of Sciences.   10.1073/pnas.1504985112   AbstractWebsite

Ray-finned fishes (Actinopterygii) comprise nearly half of all modern vertebrate diversity, and are an ecologically and numerically dominant megafauna in most aquatic environments. Crown teleost fishes diversified relatively recently, during the Late Cretaceous and early Paleogene, although the exact timing and cause of their radiation and rise to ecological dominance is poorly constrained. Here we use microfossil teeth and shark dermal scales (ichthyoliths) preserved in deep-sea sediments to study the changes in the pelagic fish community in the latest Cretaceous and early Paleogene. We find that the Cretaceous−Paleogene (K/Pg) extinction event marked a profound change in the structure of ichthyolith communities around the globe: Whereas shark denticles outnumber ray-finned fish teeth in Cretaceous deep-sea sediments around the world, there is a dramatic increase in the proportion of ray-finned fish teeth to shark denticles in the Paleocene. There is also an increase in size and numerical abundance of ray-finned fish teeth at the boundary. These changes are sustained through at least the first 24 million years of the Cenozoic. This new fish community structure began at the K/Pg mass extinction, suggesting the extinction event played an important role in initiating the modern “age of fishes.”

Yamaguchi, T, Norris RD.  2015.  No place to retreat: Heavy extinction and delayed recovery on a Pacific guyot during the Paleocene-Eocene Thermal Maximum. Geology. 43:443-446.   10.1130/g36379.1   AbstractWebsite

Modern global change threatens alpine ecosystems by forcing species to migrate to higher elevations and potentially eliminating alpine habitat altogether. Here we show that an analogous restriction of suitable habitat operates on submarine mountains. During the Paleocene-Eocene Thermal Maximum (PETM, ca. 55.96 Ma), ostracodes underwent local extinction on the crest of Allison Guyot in the central Pacific Ocean, which lost 64% of its ostracode species richness (14 species reduced to three species) and as much as 94% of ostracode abundance for similar to 1.1 m.y., before recolonization rebuilt biodiversity and abundance over the next 200 k.y. Biotic changes may reflect an increase in current speeds, acidification, and a decrease in food supply owing to a temperature-driven increase in metabolic rates. Notably, continental margin ostracodes also underwent extinction during the PETM (25%-38% loss) but, unlike Allison Guyot faunas, could quickly repopulate the continental slope. The absence of refugia for isolated seamounts prolonged the reduction in biodiversity initiated by the PETM, a pattern that may be expected for modern seamount faunas in an era of future global change.

Turner, SK, Sexton PF, Charles CD, Norris RD.  2014.  Persistence of carbon release events through the peak of early Eocene global warmth. Nature Geoscience. 7:748-751.   10.1038/ngeo2240   AbstractWebsite

The Early Eocene Climatic Optimum (53-50 million years ago) was preceded by approximately six million years of progressive global warming(1). This warming was punctuated by a series of rapid hyperthermal warming events triggered by the release of greenhouse gases(1-7). Over these six million years, the carbon isotope record suggests that the events became more frequent but smaller in magnitude(3,5-7). This pattern has been suggested to reflect a thermodynamic threshold for carbon release that was more easily crossed as global temperature rose, combined with a decrease in the size of carbon reservoirs during extremely warm conditions(8-11). Here we present a continuous, 4.25-million-year-long record of the stable isotope composition of carbonate sediments from the equatorial Atlantic, spanning the peak of early Eocene global warmth. A composite of this and pre-existing(7,12) records shows that the carbon isotope excursions that identify the hyperthermals exhibit continuity in magnitude and frequency throughout the approximately 10-million-year period covering the onset, peak and termination of the Early Eocene Climate Optimum. We suggest that the carbon cycle processes behind these events, excluding the largest event, the Palaeocene-Eocene Thermal Maximum (about 56 million years ago), were not exceptional. Instead, we argue that the hyperthermals may reflect orbital forcing of the carbon cycle analogous to the mechanisms proposed(13,14) to operate in the cooler Oligocene and Miocene.

Sibert, EC, Hull PM, Norris RD.  2014.  Resilience of Pacific pelagic fish across the Cretaceous/Palaeogene mass extinction. Nature Geoscience. 7:667-670.   10.1038/ngeo2227   AbstractWebsite

Open-ocean ecosystems experienced profound disruptions to biodiversity and ecological structure during the Cretaceous/Palaeogene mass extinction about 66 million years ago(1-3). It has been suggested that during this mass extinction, a collapse of phytoplankton production rippled up the food chain, causing the wholesale loss of consumers and top predators(3-5). Pelagic fish represent a key trophic link between primary producers and top predators, and changes in their abundance provide a means to examine trophic relationships during extinctions. Here we analyse accumulation rates of microscopic fish teeth and shark dermal scales (ichthyoliths) in sediments from the Pacific Ocean and Tethys Sea across the Cretaceous/Palaeogene extinction to reconstruct fish abundance. We find geographic differences in post-disaster ecosystems. In the Tethys Sea, fish abundance fell abruptly at the Cretaceous/Palaeogene boundary and remained depressed for at least 3 million years. In contrast, fish abundance in the Pacific Ocean remained at or above pre-boundary levels for at least four million years following the mass extinction, despite marked extinctions in primary producers and other zooplankton consumers in this region. We suggest that the mass extinction did not produce a uniformly dead ocean or microbially dominated system. Instead, primary production, at least regionally, supported ecosystems with mid-trophic-level abundances similar to or above those of the Late Cretaceous.

Norris, RD, Norris JM, Lorenz RD, Ray J, Jackson B.  2014.  Sliding rocks on Racetrack Playa, Death Valley National Park: First observation of rocks in motion. PLoS ONE. 9:e105948.: Public Library of Science   10.1371/journal.pone.0105948   AbstractWebsite

The engraved trails of rocks on the nearly flat, dry mud surface of Racetrack Playa, Death Valley National Park, have excited speculation about the movement mechanism since the 1940s. Rock movement has been variously attributed to high winds, liquid water, ice, or ice flotation, but has not been previously observed in action. We recorded the first direct scientific observation of rock movements using GPS-instrumented rocks and photography, in conjunction with a weather station and time-lapse cameras. The largest observed rock movement involved >60 rocks on December 20, 2013 and some instrumented rocks moved up to 224 m between December 2013 and January 2014 in multiple move events. In contrast with previous hypotheses of powerful winds or thick ice floating rocks off the playa surface, the process of rock movement that we have observed occurs when the thin, 3 to 6 mm, “windowpane” ice sheet covering the playa pool begins to melt in late morning sun and breaks up under light winds of ∼4–5 m/s. Floating ice panels 10 s of meters in size push multiple rocks at low speeds of 2–5 m/min. along trajectories determined by the direction and velocity of the wind as well as that of the water flowing under the ice.

Bornemann, A, Norris RD, Lyman JA, D'Haenens S, Groeneveld J, Rohl U, Farley KA, Speijer RP.  2014.  Persistent environmental change after the Paleocene-Eocene Thermal Maximum in the eastern North Atlantic. Earth and Planetary Science Letters. 394:70-81.   10.1016/j.epsl.2014.03.017   AbstractWebsite

The Paleocene-Eocene Thermal Maximum (PETM; similar to 56 Ma) is associated with abrupt climate change, carbon cycle perturbation, ocean acidification, as well as biogeographic shifts in marine and terrestrial biota that were largely reversed as the climatic transient waned. We report a clear exception to the behavior of the PETM as a reversing climatic transient in the eastern North Atlantic (Deep-Sea Drilling Project Site 401, Bay of Biscay) where the PETM initiates a greatly prolonged environmental change compared to other places on Earth where records exist. The observed environmental perturbation extended well past the delta C-13 recovery phase and up to 650 kyr after the PETM onset according to our extraterrestrial He-3-based age-model. We observe a strong decoupling of planktic foraminiferal delta O-18 and Mg/Ca values during the PETM delta C-13 recovery phase, which in combination with results from helium isotopes and clay mineralogy, suggests that the PETM triggered a hydrologic change in western Europe that increased freshwater flux and the delivery of weathering products to the eastern North Atlantic. This state change persisted long after the carbon-cycle perturbation had stopped. We hypothesize that either long-lived continental drainage patterns were altered by enhanced hydrological cycling induced by the PETM, or alternatively that the climate system in the hinterland area of Site 401 was forced into a new climate state that was not easily reversed in the aftermath of the PETM. (C) 2014 Elsevier B.V. All rights reserved.

Yamaguchi, T, Norris RD, Dockery DT.  2014.  Shallow-marine ostracode turnover during the Eocene-Oligocene transition in Mississippi, the Gulf Coast Plain, USA. Marine Micropaleontology. 106:10-21.   10.1016/j.marmicro.2013.11.003   AbstractWebsite

The Eocene-Oligocene transition (EOT) is associated with a major eustatic sea-level fall, sea surface cooling, change in ocean stratification, and enhanced seasonality. While these changes are well known to have significantly restructured open ocean ecosystems, comparatively little is known about how these multiple environmental changes affected coastal biotas. Here we describe ostracode faunas in shelf deposits in the Gulf Coast of Mexico through the Late Eocene to Early Oligocene, analyzing the biostratigraphy and paleoecology of ostracodes from the Mossy Grove core, Mississippi. Mossy Grove ostracode faunas suffered gradual extinction and diversity loss in the 150 kyr between 33.96 and 33.81 Ma. During the turnover, 10 of 21 species disappeared. Seven of the 12 disappearing species became extinct, while others are Lazarus taxa that later re-appeared in the Vicksburgian (similar to 33.7 Ma). During the sea-level fall associated with the Eocene/Oligocene (E/0) boundary (33.90 Ma), six of seven outer-shelf taxa disappeared, while three of four inner-shelf taxa increased in abundance. The major changes in ostracode assemblages occur during the EOT-1 and EOT-2 events prior to the Oil isotope excursion and appear to reflect a combination of impacts from eustatic sea-level fall and local enhanced surface ocean seasonality shown in stable isotope records from the St Stephen's Quarry core, Alabama. (C) 2013 Published by

Edgar, KM, Bohaty SM, Gibbs SJ, Sexton PF, Norris RD, Wilson PA.  2013.  Symbiont 'bleaching' in planktic foraminifera during the Middle Eocene Climatic Optimum. Geology. 41:15-18.   10.1130/g33388.1   AbstractWebsite

Many genera of modern planktic foraminifera are adapted to nutrient-poor (oligotrophic) surface waters by hosting photosynthetic symbionts, but it is unknown how they will respond to future changes in ocean temperature and acidity. Here we show that ca. 40 Ma, some fossil photosymbiont-bearing planktic foraminifera were temporarily 'bleached' of their symbionts coincident with transient global warming during the Middle Eocene Climatic Optimum (MECO). At Ocean Drilling Program (ODP) Sites 748 and 1051 (Southern Ocean and mid-latitude North Atlantic, respectively), the typically positive relationship between the size of photosymbiont-bearing planktic foraminifer tests and their carbon isotope ratios (delta C-13) was temporarily reduced for similar to 100 k.y. during the peak of the MECO. At the same time, the typically photosymbiont-bearing planktic foraminifera Acarinina suffered transient reductions in test size and relative abundance, indicating ecological stress. The coincidence of minimum delta O-18 values and reduction in test size-delta C-13 gradients suggests a link between increased sea-surface temperatures and bleaching during the MECO, although changes in pH and nutrient availability may also have played a role. Our findings show that host-photosymbiont interactions are not constant through geological time, with implications for both the evolution of trophic strategies in marine plankton and the reliability of geochemical proxy records generated from symbiont-bearing planktic foraminifera.

Norris, RD, Turner SK, Hull PM, Ridgwell A.  2013.  Marine ecosystem responses to cenozoic global change. Science. 341:492-498.   10.1126/science.1240543   AbstractWebsite

The future impacts of anthropogenic global change on marine ecosystems are highly uncertain, but insights can be gained from past intervals of high atmospheric carbon dioxide partial pressure. The long-term geological record reveals an early Cenozoic warm climate that supported smaller polar ecosystems, few coral-algal reefs, expanded shallow-water platforms, longer food chains with less energy for top predators, and a less oxygenated ocean than today. The closest analogs for our likely future are climate transients, 10,000 to 200,000 years in duration, that occurred during the long early Cenozoic interval of elevated warmth. Although the future ocean will begin to resemble the past greenhouse world, it will retain elements of the present "icehouse" world long into the future. Changing temperatures and ocean acidification, together with rising sea level and shifts in ocean productivity, will keep marine ecosystems in a state of continuous change for 100,000 years.