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2017
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.

2016
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.

2015
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.

2014
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

2013
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.

Addison, JA, Finney BP, Jaeger JM, Stoner JS, Norris RD, Hangsterfer A.  2013.  Integrating satellite observations and modern climate measurements with the recent sedimentary record: An example from Southeast Alaska. Journal of Geophysical Research-Oceans. 118:3444-3461.   10.1002/jgrc.20243   AbstractWebsite

Assessments of climate change over time scales that exceed the last 100 years require robust integration of high-quality instrument records with high-resolution paleoclimate proxy data. In this study, we show that the recent biogenic sediments accumulating in two temperate ice-free fjords in Southeast Alaska preserve evidence of North Pacific Ocean climate variability as recorded by both instrument networks and satellite observations. Multicore samples EW0408-32MC and EW0408-43MC were investigated with Cs-137 and excess Pb-210 geochronometry, three-dimensional computed tomography, high-resolution scanning XRF geochemistry, and organic stable isotope analyses. EW0408-32MC (57.162 degrees N, 135.357 degrees W, 146 m depth) is a moderately bioturbated continuous record that spans AD approximate to 1930-2004. EW0408-43MC (56.965 degrees N, 135.268 degrees W, 91 m depth) is composed of laminated diatom oozes, a turbidite, and a hypopycnal plume (river flood) deposit. A discontinuous event-based varve chronology indicates 43MC spans AD approximate to 1940-1981. Decadal-scale fluctuations in sedimentary Br/Cl ratios accurately reflect changes in marine organic matter accumulation that display the same temporal pattern as that of the Pacific Decadal Oscillation. An estimated Sitka summer productivity parameter calibrated using SeaWiFS satellite observations support these relationships. The correlation of North Pacific climate regime states, primary productivity, and sediment geochemistry indicate the accumulation of biogenic sediment in Southeast Alaska temperate fjords can be used as a sensitive recorder of past productivity variability, and by inference, past climate conditions in the high-latitude Gulf of Alaska.

Carilli, JE, Charles CD, Garren M, McField M, Norris RD.  2013.  Baseline shifts in coral skeletal oxygen isotopic composition: a signature of symbiont shuffling? Coral Reefs. 32:559-571.   10.1007/s00338-012-1004-y   AbstractWebsite

Decades-long records of the stable isotopic composition of coral skeletal cores were analyzed from four sites on the Mesoamerican Reef. Two of the sites exhibited baseline shifts in oxygen isotopic composition after known coral bleaching events. Changes in pH at the calcification site caused by a change in the associated symbiont community are invoked to explain the observed shift in the isotopic composition. To test the hypothesis that changes in symbiont clade could affect skeletal chemistry, additional coral samples were collected from Belize for paired Symbiodinium identification and skeletal stable isotopic analysis. We found some evidence that skeletal stable isotopic composition may be affected by symbiont clade and suggest this is an important topic for future investigation. If different Symbiodinium clades leave consistent signatures in skeletal geochemical composition, the signature will provide a method to quantify past symbiont shuffling events, important for understanding how corals are likely to respond to climate change.

Forrest, MJ, Kulongoski JT, Edwards MS, Farrar CD, Belitz K, Norris RD.  2013.  Hydrothermal contamination of public supply wells in Napa and Sonoma Valleys, California. Applied Geochemistry. 33:25-40.   10.1016/j.apgeochem.2013.01.012   AbstractWebsite

Groundwater chemistry and isotope data from 44 public supply wells in the Napa and Sonoma Valleys, California were determined to investigate mixing of relatively shallow groundwater with deeper hydrothermal fluids. Multivariate analyses including Cluster Analyses, Multidimensional Scaling (MDS), Principal Components Analyses (PCA), Analysis of Similarities (ANOSIM), and Similarity Percentage Analyses (SIMPER) were used to elucidate constituent distribution patterns, determine which constituents are significantly associated with these hydrothermal systems, and investigate hydrothermal contamination of local groundwater used for drinking water. Multivariate statistical analyses were essential to this study because traditional methods, such as mixing tests involving single species (e. g. Cl or SiO2) were incapable of quantifying component proportions due to mixing of multiple water types. Based on these analyses, water samples collected from the wells were broadly classified as fresh groundwater, saline waters, hydrothermal fluids, or mixed hydrothermal fluids/meteoric water wells. The Multivariate Mixing and Mass-balance (M3) model was applied in order to determine the proportion of hydrothermal fluids, saline water, and fresh groundwater in each sample. Major ions, isotopes, and physical parameters of the waters were used to characterize the hydrothermal fluids as Na-Cl type, with significant enrichment in the trace elements As, B, F and Li. Five of the wells from this study were classified as hydrothermal, 28 as fresh groundwater, two as saline water, and nine as mixed hydrothermal fluids/meteoric water wells. The M3 mixing-model results indicated that the nine mixed wells contained between 14% and 30% hydrothermal fluids. Further, the chemical analyses show that several of these mixed-water wells have concentrations of As, F and B that exceed drinking-water standards or notification levels due to contamination by hydrothermal fluids. (C) 2013 Elsevier Ltd. All rights reserved.

2012
Norris, RD, Hull PM.  2012.  The temporal dimension of marine speciation. Evolutionary Ecology. 26:393-415.   10.1007/s10682-011-9488-4   AbstractWebsite

Speciation is a process that occurs over time and, as such, can only be fully understood in an explicitly temporal context. Here we discuss three major consequences of speciation's extended duration. First, the dynamism of environmental change indicates that nascent species may experience repeated changes in population size, genetic diversity, and geographic distribution during their evolution. The present characteristics of species therefore represents a static snapshot of a single time point in a species' highly dynamic history, and impedes inferences about the strength of selection or the geography of speciation. Second, the process of speciation is open ended-ecological divergence may evolve in the space of a few generations while the fixation of genetic differences and traits that limit outcrossing may require thousands to millions of years to occur. As a result, speciation is only fully recognized long after it occurs, and short-lived species are difficult to discern. Third, the extinction of species or of clades provides a simple, under-appreciated, mechanism for the genetic, biogeographic, and behavioral 'gaps' between extant species. Extinction also leads to the systematic underestimation of the frequency of speciation and the overestimation of the duration of species formation. Hence, it is no surprise that a full understanding of speciation has been difficult to achieve. The modern synthesis-which united genetics, development, ecology, biogeography, and paleontology-greatly advanced the study of evolution. Here we argue that a similarly synthetic approach must be taken to further our understanding of the origin of species.

Larrasoana, JC, Roberts AP, Chang L, Schellenberg SA, Gerald JDF, Norris RD, Zachos JC.  2012.  Magnetotactic bacterial response to Antarctic dust supply during the Palaeocene-Eocene thermal maximum. Earth and Planetary Science Letters. 333:122-133.   10.1016/j.epsl.2012.04.003   AbstractWebsite

Distinct magnetic properties of marine sediments that record the Palaeocene-Eocene thermal maximum (PETM) have been suggested to be due to a bacterial magnetofossil signal that is linked to enhanced weathering conditions during the PETM. We document the dominance of bacterial magnetite in deep-sea sediments from southern Kerguelen Plateau (Ocean Drilling Program Hole 738C, southern Ocean) not only during the PETM, but also before and after the thermal event. This occurrence of magnetofossils throughout the PETM indicates that the occurrence of bacterial magnetosomes is not due to a preservation effect. Instead, we suggest that it is due to sustained mild iron-reducing conditions that dissolved the most labile aeolian-derived iron, which favoured continued magnetotactic bacterial activity without being strong enough to dissolve the less reactive magnetite and haematite. Enhanced aeolian haematite abundances at the beginning of the PETM indicate drier conditions on the neighbouring Antarctic continent at those times. Our results provide evidence that iron fertilisation by aeolian dust was the main limiting factor that conditioned proliferation of magnetotactic bacteria in the deep sea at the southern Kerguelen Plateau, with the exception of two short periods of rapidly changing palaeoenvironmental conditions at the onset and termination of the PETM. Increased iron supply from aeolian dust, that enhanced oceanic primary productivity and subsequent delivery of organic carbon to the seafloor, along with mild iron-reducing diagenetic conditions, seem to have been necessary to provide the iron needed for magnetite biomineralization by magnetotactic bacteria to drive their marked increase in abundance in the studied PETM record from southern Kerguelen Plateau. Our analyses of a deep-sea PETM record from Hole 1051B at Blake Nose (Atlantic Ocean) failed to identify magnetofossils despite evidence for the occurrence of magnetite and haematite of probable aeolian origin. Contrasting magnetic properties at these PETM sections indicate that further work is needed to understand the palaeoenvironmental and diagenetic factors whose interactions lead to production and preservation of magnetofossils in deep-sea sediments. (C) 2012 Elsevier B.V. All rights reserved.

Freeman, LA, Miller AJ, Norris RD, Smith JE.  2012.  Classification of remote Pacific coral reefs by physical oceanographic environment. Journal of Geophysical Research-Oceans. 117   10.1029/2011jc007099   AbstractWebsite

The oceanographic environment is a key element in structuring coral reef ecosystems by setting the range of physical and chemical conditions in which coral reef-builders live. A cluster analysis of physical and chemical oceanographic data is used to classify coral habitats in the remote tropical and subtropical Pacific Ocean based on average temperature, temperature seasonal cycle, nutrient levels, salinity, aragonite saturation state, storm frequency, intense hurricane hits, and dissolved oxygen as well as temperature anomalies in degree heating weeks. The resulting seven geographic habitats are stable to perturbations in types of data used in the cluster analysis. Based on recent coral reef survey data in the area, the coral cover was related to the identified geographic regions. The habitats tend to be geographically clustered, and each is characterized by a unique combination of oceanographic conditions. Previous studies suggest coral reef habitats are associated with a uniform array of oceanographic conditions, while our results demonstrate that finer-scale variations in physical variables may control coral reef environments. The results better define the physical environment of remote coral reefs, forming a foundation for future work addressing physical habitat perturbation and anthropogenic impacts on reefs.

Friedrich, O, Norris RD, Erbacher J.  2012.  Evolution of middle to Late Cretaceous oceans-A 55 m.y. record of Earth's temperature and carbon cycle. Geology. 40:107-110.   10.1130/g32701.1   AbstractWebsite

A new 55 m.y. global compilation of benthic foraminifera delta C-13 and delta O-18 for the middle to Late Cretaceous shows that there was widespread formation of bottom waters with temperatures >20 degrees C during the Cretaceous greenhouse world. These bottom waters filled the silled North Atlantic and probably originated as thermocline or intermediate waters in the tropical oceans. Carbon burial during the Cretaceous oceanic anoxic events produced a positive delta C-13 shift in global carbon reservoirs, but this is not particularly large, especially by comparison with the remarkable Late Paleocene carbon maximum. The interbasin delta C-13 gradient was unusually large during the Cretaceous hot greenhouse, probably because the North Atlantic sills prevented the free exchange of waters in the deep basin. The hot greenhouse ended when the Equatorial Atlantic Gateway opened sufficiently to flood the deep North Atlantic with relatively cool polar waters formed in the Southern Ocean.