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2019
McCormick, LR, Levin LA, Oesch NW.  2019.  Vision is highly sensitive to oxygen availability in marine invertebrate larvae. Journal of Experimental Biology. 222   10.1242/jeb.200899   AbstractWebsite

For many animals, evolution has selected for complex visual systems despite the high energetic demands associated with maintaining eyes and their processing structures. Therefore, the metabolic demands of visual systems make them highly sensitive to fluctuations in available oxygen. In the marine environment, oxygen changes over daily, seasonal and inter-annual time scales, and there are large gradients of oxygen with depth. Vision is linked to survival in many marine animals, particularly among the crustaceans, cephalopods and fish, and early life stages of these groups rely on vision for prey capture, predator detection and their distribution in the water column. Using in vivo electroretinogram recordings, we show that there is a decrease in retinal sensitivity to light in marine invertebrates when exposed to reduced oxygen availability. We found a 60-100% reduction in retinal responses in the larvae of cephalopods and crustaceans: the market squid (Doryteuthis opalescens), the two-spot octopus (Octopus bimaculatus), the tuna crab (Pleuroncodes planipes) and the graceful rock crab (Metacarcinus gracilis). A decline in oxygen also decreases the temporal resolution of vision in D. opalescens. These results are the first demonstration that vision in marine invertebrates is highly sensitive to oxygen availability and that the thresholds for visual impairment from reduced oxygen are species-specific. Oxygen-impaired retinal function may change the visual behaviors crucial to survival in these marine larvae. These findings may impact our understanding of species' vulnerability to ocean oxygen loss and suggest that researchers conducting electrophysiology experiments should monitor oxygen levels, as even small changes in oxygen may affect the results.

2017
McCormick, LR, Levin LA.  2017.  Physiological and ecological implications of ocean deoxygenation for vision in marine organisms. Philosophical Transactions of the Royal Society a-Mathematical Physical and Engineering Sciences. 375   10.1098/rsta.2016.0322   AbstractWebsite

Climate change has induced ocean deoxygenation and exacerbated eutrophication-driven hypoxia in recent decades, affecting the physiology, behaviour and ecology of marine organisms. The high oxygen demand of visual tissues and the known inhibitory effects of hypoxia on human vision raise the questions if and how ocean deoxygenation alters vision in marine organisms. This is particularly important given the rapid loss of oxygen and strong vertical gradients in oxygen concentration in many areas of the ocean. This review evaluates the potential effects of low oxygen (hypoxia) on visual function in marine animals and their implications for marine biota under current and future ocean deoxygenation based on evidence from terrestrial and a few marine organisms. Evolutionary history shows radiation of eye designs during a period of increasing ocean oxygenation. Physiological effects of hypoxia on photoreceptor function and light sensitivity, in combination with morphological changes that may occur throughout ontogeny, have the potential to alter visual behaviour and, subsequently, the ecology of marine organisms, particularly for fish, cephalopods and arthropods with `fast' vision. Visual responses to hypoxia, including greater light requirements, offer an alternative hypothesis for observed habitat compression and shoaling vertical distributions in visual marine species subject to ocean deoxygenation, which merits further investigation. This article is part of the themed issue 'Ocean ventilation and deoxygenation in a warming world'.

2016
Levin, LA, Mengerink K, Gjerde KM, Rowden AA, Vandover CL, Clark MR, Ramirez-Llodra E, Currie B, Smith CR, Sato KN, Gallo N, Sweetman AK, Lily H, Armstrong CW, Brider J.  2016.  Defining "serious harm" to the marine environment in the context of deep-seabed mining. Marine Policy. 74:245-259.   10.1016/j.marpol.2016.09.032   AbstractWebsite

Increasing interest in deep-seabed mining has raised many questions surrounding its potential environmental impacts and how to assess the impacts' significance. Under the United Nations Convention on the Law of the Sea (UNCLOS), the International Seabed Authority (ISA) is charged with ensuring effective protection of the marine environment as part of its responsibilities for managing mining in seabed areas beyond national jurisdiction (the Area) on behalf of humankind. This paper examines the international legal context for protection of the marine environment and defining the significant adverse change that can cause "serious harm", a term used in the ISA Mining Code to indicate a level of harm that strong actions must be taken to avoid. It examines the thresholds and indicators that can reflect significant adverse change and considers the specific vulnerability of the four ecosystems associated with the minerals targeted for mining: (1) manganese (polymetallic) nodules, (2) seafloor massive (polymetallic) sulphides, (3) cobalt-rich (polymetallic) crusts and (4) phosphorites. The distributions and ecological setting, probable mining approaches and the potential environmental impacts of mining are examined for abyssal polymetallic nodule provinces, hydrothermal vents, seamounts and phosphorite-rich continental margins. Discussion focuses on the special features of the marine environment that affect the significance of the predicted environmental impacts and suggests actions that will advance understanding of these impacts.

Navarro, MO, Kwan GT, Batalov O, Choi CY, Pierce NT, Levin LA.  2016.  Development of embryonic market squid, Doryteuthis opalescens, under chronic exposure to low environmental pH and O-2. Plos One. 11   10.1371/journal.pone.0167461   AbstractWebsite

The market squid, Doryteuthis opalescens, is an important forage species for the inshore ecosystems of the California Current System. Due to increased upwelling and expansion of the oxygen minimum zone in the California Current Ecosystem, the inshore environment is expected to experience lower pH and [O-2] conditions in the future, potentially impacting the development of seafloor-attached encapsulated embryos. To understand the consequences of this co-occurring environmental pH and [O-2] stress for D. opalescens encapsulated embryos, we performed two laboratory experiments. In Experiment 1, embryo capsules were chronically exposed to a treatment of higher (normal) pH (7.93) and [O-2] (242 mu M) or a treatment of low pH (7.57) and [O-2] (80 mu M), characteristic of upwelling events and/or La Nina conditions. The low pH and low [O-2] treatment extended embryo development duration by 5-7 days; embryos remained at less developed stages more often and had 54.7% smaller statolith area at a given embryo size. Importantly, the embryos that did develop to mature embryonic stages grew to sizes that were similar (non-distinct) to those exposed to the high pH and high [O-2] treatment. In Experiment 2, we exposed encapsulated embryos to a single stressor, low pH (7.56) or low [O-2] (85 mu M), to understand the importance of environmental pH and [O-2] rising and falling together for squid embryogenesis. Embryos in the low pH only treatment had smaller yolk reserves and bigger statoliths compared to those in low [O-2] only treatment. These results suggest that D. opalescens developmental duration and statolith size are impacted by exposure to environmental [O-2] and pH (pCO(2)) and provide insight into embryo resilience to these effects.

2015
Neira, C, Mendoza G, Porrachia M, Stransky C, Levin LA.  2015.  Macrofaunal recolonization of copper-contaminated sediments in San Diego Bay. Marine Pollution Bulletin. 101:794-804.   10.1016/j.marpolbul.2015.09.023   AbstractWebsite

Effects of Cu-loading on macrofaunal recolonization were examined in Shelter Island Yacht Basin (San Diego Bay, California). Sediments with high and low Cu levels were defaunated and Cu-spiked, translocated, and then placed back into the environment These demonstrated that the alteration observed in benthic communities associated with Cu contamination occurs during initial recolonization. After a 3-month exposure to sediments with varying Cu levels, two primary colonizing communities were identified: (1) a "mouth assemblage" resembling adjacent background fauna associated with low-Cu levels that was more diverse and predominantly dominated by surface- and subsurface-deposit feeders, burrowers, and tube builders, and (2) a "head assemblage" resembling adjacent background fauna associated with high-Cu concentrations, with few dominant species and an increasing importance of carnivores and mobile epifauna. Cu loading can cause reduced biodiversity and lower structural complexity that may last several months if high concentrations persist, with a direct effect on community functioning. (C) 2015 Elsevier Ltd. All rights reserved.

Levin, LA, Liu KK, Emeis KC, Breitburg DL, Cloern J, Deutsch C, Giani M, Goffart A, Hofmann EE, Lachkar Z, Limburg K, Liu SM, Montes E, Naqvi W, Ragueneau O, Rabouille C, Sarkar SK, Swaney DP, Wassman P, Wishner KF.  2015.  Comparative biogeochemistry-ecosystem-human interactions on dynamic continental margins. Journal of Marine Systems. 141:3-17.   10.1016/j.jmarsys.2014.04.016   AbstractWebsite

The oceans' continental margins face strong and rapid change, forced by a combination of direct human activity, anthropogenic CO2-induced climate change, and natural variability. Stimulated by discussions in Goa, India at the IMBER IMBIZO III, we (1) provide an overview of the drivers of biogeochemical variation and change on margins, (2) compare temporal trends in hydrographic and biogeochemical data across different margins, (3) review ecosystem responses to these changes, (4) highlight the importance of margin time series for detecting and attributing change and (5) examine societal responses to changing margin biogeochemistry and ecosystems. We synthesize information over a wide range of margin settings in order to identify the commonalities and distinctions among continental margin ecosystems. Key drivers of biogeochemical variation include long-term climate cycles, CO2-induced warming, acidification, and deoxygenation, as well as sea level rise, eutrophication, hydrologic and water cycle alteration, changing land use, fishing, and species invasion. Ecosystem responses are complex and impact major margin services. These include primary production, fisheries production, nutrient cycling, shoreline protection, chemical buffering, and biodiversity. Despite regional differences, the societal consequences of these changes are unarguably large and mandate coherent actions to reduce, mitigate and adapt to multiple stressors on continental margins. (C) 2014 Elsevier BM. All rights reserved.

2011
Ramirez-Llodra, E, Tyler PA, Baker MC, Bergstad OA, Clark MR, Escobar E, Levin LA, Menot L, Rowden AA, Smith CR, Vandover CL.  2011.  Man and the last great wilderness: human impact on the deep sea. Plos One. 6   10.1371/journal.pone.0022588   AbstractWebsite

The deep sea, the largest ecosystem on Earth and one of the least studied, harbours high biodiversity and provides a wealth of resources. Although humans have used the oceans for millennia, technological developments now allow exploitation of fisheries resources, hydrocarbons and minerals below 2000 m depth. The remoteness of the deep seafloor has promoted the disposal of residues and litter. Ocean acidification and climate change now bring a new dimension of global effects. Thus the challenges facing the deep sea are large and accelerating, providing a new imperative for the science community, industry and national and international organizations to work together to develop successful exploitation management and conservation of the deep-sea ecosystem. This paper provides scientific expert judgement and a semi-quantitative analysis of past, present and future impacts of human-related activities on global deep-sea habitats within three categories: disposal, exploitation and climate change. The analysis is the result of a Census of Marine Life - SYNDEEP workshop (September 2008). A detailed review of known impacts and their effects is provided. The analysis shows how, in recent decades, the most significant anthropogenic activities that affect the deep sea have evolved from mainly disposal (past) to exploitation (present). We predict that from now and into the future, increases in atmospheric CO(2) and facets and consequences of climate change will have the most impact on deep-sea habitats and their fauna. Synergies between different anthropogenic pressures and associated effects are discussed, indicating that most synergies are related to increased atmospheric CO(2) and climate change effects. We identify deep-sea ecosystems we believe are at higher risk from human impacts in the near future: benthic communities on sedimentary upper slopes, cold-water corals, canyon benthic communities and seamount pelagic and benthic communities. We finalise this review with a short discussion on protection and management methods.

2009
Basak, C, Rathburn AE, Perez ME, Martin JB, Kluesner JW, Levin LA, De Deckker P, Gieskes JM, Abriani M.  2009.  Carbon and oxygen isotope geochemistry of live (stained) benthic foraminifera from the Aleutian Margin and the Southern Australian Margin. Marine Micropaleontology. 70:89-101.   10.1016/j.marmicro.2008.11.002   AbstractWebsite

Comparisons of ambient bottom-water geochemistry and stable isotopic values of the tests of living (stained) calcareous benthic foraminifera from the North Pacific (on the Aleutian Margin, water depth 1988 m) and Murray Canyons group in the Southern Indian Ocean (Australian Margin, water depths 2476 m and 1634 m) provide modem environmental analogs to calibrate paleoenvironmental assessments. Consistent with the hypothesis that microhabitat preferences influence foraminiferal isotopic values, benthic foraminifera from both margins were depleted in (13)C with respect to bottom-water dissolved inorganic carbon (DIC). The carbon isotope values of deep infaunal foraminifera (Chilostomella oolina, Globobulimina pacifica) showed greater differences from estimates of those of DIC than shallow benthic foraminifera (Bulimina mexicana, Bolivinita quadrilatera, Pullenia bulloides). This study provides new isotopic and ecological information for B. quadrilatera. The mean Delta delta(13)C value, defined as foraminiferal delta(13)C values minus estimated ambient delta(13)C values from the Aleutian Margin, is 0.97 parts per thousand higher for G. pacifica than the mean from the Murray Canyon. This difference may result either from genetic or biological differences between the populations or from differences in environmental isotopic influences (such as pore water differences) that were not accounted for in the equilibrium calculations. These analyses provide calibration information for the evaluation of bottom water conditions and circulation patterns of ancient oceans based on fossil foraminiferal geochemistry. (C) 2008 Elsevier B.V. All rights reserved.

Hughes, DJ, Lamont PA, Levin LA, Packer M, Feeley K, Gage JD.  2009.  Macrofaunal communities and sediment structure across the Pakistan margin Oxygen Minimum Zone, North-East Arabian Sea. Deep-Sea Research Part Ii-Topical Studies in Oceanography. 56:434-448.   10.1016/j.dsr2.2008.05.030   AbstractWebsite

Benthic macrofauna and sediment column features were sampled at five stations along a bathymetric transect (depths 140, 300, 940, 1200, 1850 m) through the Pakistan margin Oxygen Minimum Zone (OMZ) during the 2003 intermonsoon (March-May) and late-post-monsoon (August-October) periods. Objectives were to compare patterns with those described from other OMZs, particularly the Oman margin of the Arabian Sea, in order to assess the relative influence of bottom-water oxygenation and sediment organic content on macrofaunal standing stock and community structure. Macrofaunal density was highest at the 140-m station subject to monsoon-driven shoaling of the OMZ, but there was no elevation of density at the lower OMZ boundary (1200 m). Numbers was extremely low in the OMZ core (300 m) and were not readily explicable from the environmental data. There was no consistent depth-related trend in macrofaunal biomass. Macrofaunal densities were consistently lower than found off Oman but there was less contrast in biomass. A significant post-monsoon decline in macrofaunal density at 140 m was driven by selective loss of polychaete taxa. Polychaeta was the most abundant major taxon at all stations but did not dominate the macrofaunal community to the extent reported from Oman. Cirratulidae and Spionidae were major components of the polychaete fauna at most stations but Acrocirridae, Ampharetidae, Amphinomidae and Cossuridae were more important at 940 m. Polychaete assemblages at each station were almost completely distinct at the species level. Polychaete species richness was positively correlated with bottom-water dissolved oxygen and negatively correlated with sediment TOC, C:N ratio and total phytopigments. Community dominance showed the opposite pattern. The strongly inverse correlation between oxygen and measures of sediment organic content made it difficult to distinguish their relative effects. The strongly laminated sediments in the OMZ core contrasted with the homogeneous, heavily bioturbated sediments above and below this zone but were associated with minimal macrofaunal biomass rather than distinctive functional group composition. In general, data from the Oman margin were weak predictors of patterns seen off Pakistan, and results suggest the importance of local factors superimposed on the broader trends of macrofaunal community composition in OMZs. (C) 2008 Elsevier Ltd. All rights reserved.

Fodrie, FJ, Levin LA, Rathburn AE.  2009.  High densities and depth-associated changes of epibenthic megafauna along the Aleutian margin from 2000-4200 m. Journal of the Marine Biological Association of the United Kingdom. 89:1517-1527.   10.1017/s0025315409000903   AbstractWebsite

The Aleutian margin is a dynamic environment underlying a productive coastal ocean and subject to frequent tectonic disturbance. In July 2004, We used over 500 individual bottom images from towed camera transects to investigate patterns of epibenthic megafaunal density and community composition on the contiguous Aleutian margin (53 degrees N 163 degrees W) at depths of 2000 m, 3200 m and 4200 M. We also examined the influence of vertical isolation on the megafaunal assemblage across a topographic rise at 3200 m, located 30 km from the main margin and elevated 800 m above the surrounding seafloor. In comparison to previous reports from bathyal and abyssal depths, megafaunal densities along the Aleutian margin were remarkably high, averaging 5.38 +/- 0.43 (mean +/- 1 standard error), 0.32 +/- 0.02 to 0.43 +/- 0.03 and 0.27 +/- 0.01 individuals m(-2) at 2000 m, 3200 m and 4200 m, respectively. Diversity at 2000 M Was elevated by 15-30% over the deeper sites (3200-4200 m) depending on the metric, while evenness was depressed by similar to 10%. Levels of richness and evenness were similar among the three deeper sites. Echinoderms were the most abundant phylum at each depth; ophiuroids accounted for 89% of individuals in photographs at 2000 m, echinoids were dominant at 3200 M (39%), and holothurians dominated at 4200 m (47%). We observed a 26% reduction in megafaunal density across the summit of the topographic rise relative to that documented on the continental slope at the same depth. However, the two communities at 3200 m were very similar in composition. Together, these data support the modified 'archibenthal zone of transition' framework for slope community patterns with distinct communities along the middle and lower slope (the upper slope was not evaluated here). This study fills a geographical gap by providing baseline information for a relatively pristine, high-latitude, deep-sea benthic ecosystem. As pressures grow for drilling, fishing and mining on high-latitude margins, such data can serve as a reference point for much-needed studies on the ecology, long-term dynamics, and anthropogenically induced change of these habitats.

2004
Helly, JJ, Levin LA.  2004.  Global distribution of naturally occurring marine hypoxia on continental margins. Deep-Sea Research Part I-Oceanographic Research Papers. 51:1159-1168.   10.1016/j.dsr.2004.03.009   AbstractWebsite

Hypoxia in the ocean influences biogeochemical cycling of elements, the distribution of marine species and the economic well being of many coastal countries. Previous delineations of hypoxic environments focus on those in enclosed seas where hypoxia may be exacerbated by anthropogenically induced eutrophication. Permanently hypoxic water masses in the open ocean, referred to as oxygen minimum zones, impinge on a much larger seafloor surface area along continental margins of the eastern Pacific, Indian and western Atlantic Oceans. We provide the first global quantification of naturally hypoxic continental margin floor by determining upper and lower oxygen minimum zone depth boundaries from hydrographic data and computing the area between the isobaths using seafloor topography. This approach reveals that there are over one million km(2) of permanently hypoxic shelf and bathyal sea floor, where dissolved oxygen is <0.5ml l(-1); over half (59%) occurs in the northern Indian Ocean. We also document strong variation in the intensity, vertical position and thickness of the OMZ as a function of latitude in the eastern Pacific Ocean and as a function of longitude in the northern Indian Ocean. Seafloor OMZs are regions of low biodiversity and are inhospitable to most commercially valuable marine resources, but support a fascinating array of protozoan and metazoan adaptations to hypoxic conditions. (C) 2004 Elsevier Ltd. All rights reserved.

2000
Smith, CR, Levin LA, Hoover DJ, McMurtry G, Gage JD.  2000.  Variations in bioturbation across the oxygen minimum zone in the northwest Arabian Sea. Deep-Sea Research Part Ii-Topical Studies in Oceanography. 47:227-257.   10.1016/s0967-0645(99)00108-3   AbstractWebsite

Oxygen minimum zones are expected to alter substantially the nature, rates and depths of bioturbation along continental margins, yet these effects remain poorly studied. Using excess (210)Pb profiles, sediment X-radiography and box-core samples for macrofauna, we examined bioturbation processes at six stations (400, 700, 850, 1000, 1250 and 3400 m deep) along a transect across the oxygen minimum zone (OMZ) on the Oman margin. Bottom-water oxygen concentrations ranged from similar to 0.13 mi l(-1) at 400 m to similar to 2.99 mi l(-1) at 3400 m. (210)Pb mixed-layer depth and bioturbation intensity (D(b)) exhibited high within-station variance, and means did not differ significantly among stations. However, the mean mixed-layer depth (4.6 cm) for pooled OMZ stations (400-1000 m depths, 0.13-0.27 mi l(-1) bottom-water oxygen) was half that for stations from similar water depths along well-oxygenated Atlantic and Pacific slopes (11.1 cm), suggesting that oxygen stress reduced (210)Pb mixing depth on the Oman margin. Modal burrow diameter and the diversity of burrow types at a station were highly correlated with bottom-water oxygen concentration from the edge to the core of the Oman OMZ (Spearman's rho greater than or equal to 0.89, p less than or equal to 0.02), suggesting that these parameters are useful proxies for bottom-water oxygen concentrations under dysaerobic conditions. In contrast, neither the maximum diameter and nor the maximum penetration depth of open burrows exhibited oxygen-related patterns along the transect. Reduced (210)Pb mixing depth within the Oman-margin OMZ appeared to result from a predominance of surface-deposit feeders and tube builders within this zone, rather than from simple changes in horizontal or vertical distributions of macrofaunal abundance or biomass. The number of burrow types per station was highly correlated with macrofaunal species diversity, suggesting that burrow diversity may be a good proxy for species diversity in paleo-dysaerobic assemblages. We conclude that bottom-water oxygen concentrations of 0.13-0.27 mi l(-1) substantially alter a number of bioturbation parameters of importance to diagenetic and biofacies models for continental margins. (C) 1999 Elsevier Science Ltd. All rights reserved.

1997
Levin, L, Blair N, DeMaster D, Plaia G, Fornes W, Martin C, Thomas C.  1997.  Rapid subduction of organic matter by maldanid polychaetes on the North Carolina slope. Journal of Marine Research. 55:595-611.   10.1357/0022240973224337   AbstractWebsite

In situ tracer experiments conducted on the North Carolina continental slope reveal that tube-building worms (Polychaeta: Maldanidae) can, without ingestion, rapidly subduct freshly deposited, algal carbon (C-13-labeled diatoms) and inorganic materials (slope sediment and glass beads) to depths of 10 cm or more in the sediment column. Transport over 1.5 days appears to be nonselective but spatially patchy, creating localized, deep hotspots. As a result of this transport, relatively fresh organic matter becomes available soon after deposition to deep-dwelling microbes and other infauna, and both aerobic and anaerobic processes may be enhanced. Comparison of tracer subduction with estimates from a diffusive mixing model using Th-234-based coefficients, suggests that maldanid subduction activities, within 1.5 d of particle deposition, could account for 25-100% of the mixing below 5 cm that occurs on 100-day time scales. Comparisons of community data from the North Carolina slope for different places and times indicate a correlation between the abundance of deep-dwelling maldanids and the abundance and the dwelling depth in the sediment column of other infauna. Pulsed inputs of organic matter occur frequently in margin environments and maldanid polychaetes are a common component of continental slope macrobenthos. Thus, the activities we observe are likely to be widespread and significant for chemical cycling (natural and anthropogenic materials) on the slope. We propose that species like maldanids, that rapidly redistribute labile organic matter within the seabed, probably function as keystone resource modifiers. They may exert a disproportionately strong influence (relative to their abundance) on the structure of infaunal communities and on the timing, location and nature of organic matter diagenesis and burial in continental margin sediments.

1996
Blair, NE, Levin LA, Demaster DJ, Plaia G.  1996.  The short-term fate of fresh algal carbon in continental slope sediments. Limnology and Oceanography. 41:1208-1219. AbstractWebsite

Emplacement of a tracer mixture containing C-13-labeled green algae on the sea floor of the continental slope offshore of Cape Hatteras, North Carolina, elicited a rapid response over 1.5 d from the dense benthic community. Certain deposit-feeding annelids (e.g. Scalibregma inflatum and Aricidea quadrilobata) became heavily labeled with C-13 as a result Of ingestion of the algae. C-13-labeled organic matter was transported to a depth of at least 4-5 cm into the seabed during the 1.5-d period, presumably as a consequence of a feeding-associated activity. Nonlocal transport produced subsurface peaks in organic C-13 at 2-3 cm. Dissolved inorganic C-13, produced by the oxidation of the labeled algae, penetrated to 10-cm depth. The transport of highly reactive organic matter from the sediment surface at initial velocities greater than or equal to 3 cm d(-1) is expected to be an important control of subsurface benthic processes in slope environments characterized by abundant macrofaunal populations. Anaerobic processes, which are enhanced on the Cape Hatteras slope relative to adjacent areas, may be promoted by the rapid injection of reactive material into subsurface sediments. The transport, in turn, is a consequence of the dense infaunal populations that are supported by the rapid deposition of organic carbon in this region.

1995
Wishner, KF, Ashjian CJ, Gelfman C, Gowing MM, Kann L, Levin LA, Mullineaux LS, Saltzman J.  1995.  Pelagic and benthic ecology of the lower interface of the Eastern Tropical Pacific oxygen minimum zone. Deep-Sea Research Part I-Oceanographic Research Papers. 42:93-115.   10.1016/0967-0637(94)00021-j   AbstractWebsite

The distributions of pelagic and benthic fauna were examined in relation to the lower boundary of the oxygen minimum zone (OMZ) on and near Volcano 7, a seamount that penetrates this feature in the Eastern Tropical Pacific. Although the broad, pronounced OMZ in this region is an effective barrier for most zooplankton, zooplankton abundances, zooplankton feeding rates, and ambient suspended particulate organic carbon (POC) peaked sharply in the lower OMZ (about 740-800 m), in association with the minimum oxygen concentration and the increasing oxygen levels just below it. Zooplankton in the lower OMZ were also larger in size, and the pelagic community included some very abundant, possibly opportunistic, species. Elevated POC and scatter in the light transmission data suggested the existence of a thin, particle-rich, and carbon-rich pelagic layer at the base of the OMZ. Gut contents of planktonic detritivores implied opportunistic ingestion of bacterial aggregates, possibly from this layer. Benthic megafaunal abundances on the seamount, which extended up to 730 m, peaked at about 800 m. There was a consistent vertical progression in the depth of first occurrence of different megafaunal taxa in this depth range, similar to intertidal zonation. Although the vertical gradients of temperature, salinity, and oxygen were gradual at the lower OMZ interface (in contrast to the upper OMZ interface at the thermocline), temporal variability in oxygen levels due to internal wave-induced vertical excursions of the OMZ may produce the distinct zonation in the benthic fauna. The characteristics of the lower OMZ interface result from biological interactions with the chemical and organic matter gradients of the OMZ. Most zooplankton are probably excluded physiologically from pronounced OMZs. The zooplankton abundance peak at the lower interface of the OMZ occurs where oxygen becomes sufficiently high to permit the zooplankton to utilize the high concentrations of organic particles that have descended through the OMZ relatively unaltered because of low metazoan abundance. A similar scenario applies to megabenthic distributions. Plankton layers and a potential short food chain (bacteria to zooplankton) at OMZ interfaces suggest intense utilization and modification of organic material, localized within a thin midwater depth zone. This could be a potentially significant filter for organic material sinking to the deep-sea floor.

1994
Demaster, DJ, Pope RH, Levin LA, Blair NE.  1994.  Biological mixing intensity and rates of organic carbon accumulation in North Carolina slope sediments. Deep-Sea Research Part Ii-Topical Studies in Oceanography. 41:735-753.   10.1016/0967-0645(94)90045-0   AbstractWebsite

Sediment accumulation rates and biological mixing intensities were determined at three sites on the North Carolina slope based on profiles of naturally occurring C-14, Pb-210 and(234) Th. The three sites all were at a water depth of 850 m with a spacing of 150-180 km between sites. Sediment accumulation rates increase from south to north from values of 7 cm ky(-1) at Site I, to 160 cm ky(-1) at Site II, to 1100 cm ky(-1) at Site III. The organic carbon burial rate at these sites also increases in the northward direction from 0.65 (Site I) to 20 (Site II) to less than or equal to 150 g C-org m(-2) year(-1) (Site III). These data indicate that continental margin environments can exhibit highly variable carbon fluxes over relatively small distances on the seafloor. The rate of organic carbon accumulation at Site III is one of the highest values reported for the marine environment. Based on these accumulation rates and dissolved inorganic carbon flux estimates from each site, the seabed organic carbon preservation efficiency (i.e. the ratio of C-org accumulation rate to C-org deposition rate times 100) was estimated to vary from 6.0% to 54% to 88% at Sites I, II and III, respectively. The C-14 age of organic matter in surface sediments was older at Site III (1800 years BP) than at Sites I and II (800 years BP), indicating that Site III receives a greater proportion of old sediment from either up-slope areas or from terrigenous sources. Inventories of excess Th-234 (half-life of 24 days) were used as a tracer for particle flux covering the 100 days prior to the October 1989, July-August 1990 and August 1991 cruises. The mean Th-234 inventories al the three sites were 4.7 +/- 1.9, 8.4 +/- 6.3 and 23.1 +/- 7.3 dpm cm(-2) for Sites I, II and III, respectively. Profiles of excess Th-234 activity reveal that the biological mixing intensity is greater at Site III (mean D-b = 19 +/- 11 cm(2) year(-1), n = 5) than at either Site I (mean D-b = 6.0 +/- 6.2 cm(2) year(-1) n = 6) or Site II (mean D-b = 4.6 +/- 5.2 cm(2) year(-1), n = 9). In addition to the trend in mixing coefficients, the depth of particle mixing on a 100-day time scale generally is greater at Site III than at the other two sites. These observations of particle mixing intensity are consistent with the northward increase in the mean abundance of macrofauna (>300 microns) from mean values of 9400 m(-2) at Site I, to 21,400 m(-2) at Site II, to 55,500 m(-2) at Site III. For the three study sites off North Carolina, a strong correlation (R(2) = 0.99,p = 0.06) exists between macrofaunal abundance and the organic carbon deposition rate. An equally strong correlation (R(2) = 0.99, P = 0.04) occurs between macrofaunal abundance and the Th-234 inventories (index of 100-day particle flux). Fine-sand size glass tracer beads were dispersed at these three sites by submersible and then the field plots were sampled similar to 1 year later. The vertical distributions of beads at the three sites are consistent with a higher mixing intensity at Site III than at the other two sites, but the estimated mixing coefficients generally are lower than those determined from the profiles of Th-234. The slower mixing of the glass beads may be the result of their low food value and/or their relatively large size (compared to the surrounding fine-grained sediments).