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Sweetman, AK, Thurber AR, Smith CR, Levin LA, Mora C, Wei CL, Gooday AJ, Jones DOB, Rex M, Yasuhara M, Ingels J, Ruhl HA, Frieder CA, Danovaro R, Wurzberg L, Baco A, Grupe BM, Pasulka A, Meyer KS, Dunlop KM, Henry LA, Roberts JM.  2017.  Major impacts of climate change on deep-sea benthic ecosystems. Elementa-Science of the Anthropocene. 5:1-23.   10.1525/elementa.203   AbstractWebsite

The deep sea encompasses the largest ecosystems on Earth. Although poorly known, deep seafloor ecosystems provide services that are vitally important to the entire ocean and biosphere. Rising atmospheric greenhouse gases are bringing about significant changes in the environmental properties of the ocean realm in terms of water column oxygenation, temperature, pH and food supply, with concomitant impacts on deep-sea ecosystems. Projections suggest that abyssal (3000-6000 m) ocean temperatures could increase by 1 degrees C over the next 84 years, while abyssal seafloor habitats under areas of deep-water formation may experience reductions in water column oxygen concentrations by as much as 0.03 mL L-1 by 2100. Bathyal depths (200-3000 m) worldwide will undergo the most significant reductions in pH in all oceans by the year 2100 (0.29 to 0.37 pH units). O-2 concentrations will also decline in the bathyal NE Pacific and Southern Oceans, with losses up to 3.7% or more, especially at intermediate depths. Another important environmental parameter, the flux of particulate organic matter to the seafloor, is likely to decline significantly in most oceans, most notably in the abyssal and bathyal Indian Ocean where it is predicted to decrease by 40-55% by the end of the century. Unfortunately, how these major changes will affect deep-seafloor ecosystems is, in some cases, very poorly understood. In this paper, we provide a detailed overview of the impacts of these changing environmental parameters on deep-seafloor ecosystems that will most likely be seen by 2100 in continental margin, abyssal and polar settings. We also consider how these changes may combine with other anthropogenic stressors (e.g., fishing, mineral mining, oil and gas extraction) to further impact deep-seafloor ecosystems and discuss the possible societal implications.

Demaster, DJ, Thomas CJ, Blair NE, Fornes WL, Plaia G, Levin LA.  2002.  Deposition of bomb (14)C in continental slope sediments of the Mid-Atlantic Bight: assessing organic matter sources and burial rates. Deep-Sea Research Part Ii-Topical Studies in Oceanography. 49:4667-4685.   10.1016/s0967-0645(02)00134-0   AbstractWebsite

As part of the Ocean Margins Program (OMP), organic carbon (14)C measurements have been made on benthic fauna and kasten core sediments from the North Carolina continental slope. These analyses are used to evaluate the nature and burial flux of organic matter in the OMP study area off Cape Hatteras. Despite the fact that surface sediment (14)C contents ranged from -41 to -215 per mil, the benthic fauna (primarily polychactes) all contained significant amounts of bomb-(14)C (body tissue (14)C contents ranging from + 20 to + 82 per mil). Bomb-(14)C clearly is reaching the seabed on the North Carolina slope, and the labile planktonic material carrying this signal is a primary source of nutrition to the benthic ecosystem. The enrichment of (14)C in benthic faunal tissue relative to the (14)C content of bulk surface-sediment organic matter (a difference of similar to 150 per mil) is attributed to a combination of particle selection and selective digestive processes. Organic carbon burial rates from 12 stations on the North Carolina slope varied from 0.02 to 1.7 mol of Cm(-2) yr(-1), with a mean value of 0.7 mol of C m(-2) yr(-1). The accumulation of organic matter on the upper slope accounts for < 1 % of the primary production in the entire continental margin system. The North Carolina margin was deliberately selected because of its potential for offshore transport and high sediment deposition rates, and even in this environment, burial of organic carbon accounts for a very small fraction of the primary production occurring in surface waters. (C) 2002 Elsevier Science Ltd. All rights reserved.

Gage, JD, Levin LA, Wolff GA.  2000.  Benthic processes in the deep Arabian Sea: introduction and overview. Deep-Sea Research Part Ii-Topical Studies in Oceanography. 47:1-7.   10.1016/S0967-0645(99)00095-8   AbstractWebsite
Levin, LA, Gage JD, Martin C, Lamont PA.  2000.  Macrobenthic community structure within and beneath the oxygen minimum zone, NW Arabian Sea. Deep-Sea Research Part Ii-Topical Studies in Oceanography. 47:189-226.   10.1016/s0967-0645(99)00103-4   AbstractWebsite

Investigations of macrobenthos were carried out within and beneath the oxygen minimum zone (OMZ, < 0.5 ml l(-1)) during Fall 1994 on the Oman margin, NW Arabian Sea. Six stations (400, 700, 850, 1000, 1250 and 3400m) were characterized with respect to macrofaunal abundance, biomass, body size, taxonomic composition, diversity and lifestyles, and the relation of these parameters to environmental conditions. The OMZ (400-1000 m) was dominated by a dense (5818-19,183 ind m(-2)), soft-bodied assemblage consisting largely (86-99%) of surface-feeding polychaetes, Spionids and cirratulids dominated at the 400- and 700-m stations, paraonids and ampharetids at the 850- and 1000-m stations. Molluscs and most crustaceans were common only below the OMZ ( greater than or equal to 1250 m); a species of the amphipod Ampelisca was abundant within the OMZ, however. Both density and biomass were elevated within the OMZ relative to stations below but body size did not differ significantly among stations. The lower OMZ boundary (0.5 ml l(-1)) was not a zone of enhanced macrofaunal standing stock, as originally hypothesized. However, abundance maxima at 700-850m may reflect an oxygen threshold (0.15-0.20 ml l(-1)) above which macrofauna take advantage of organically enriched sediments. Incidence of burrowing and subsurface-deposit feeding increased below the OMZ, Species richness (E[S(100)]), diversity (H') and evenness (J') were lower and dominance (R1D) was higher within than beneath the OMZ. Within-station (between-boxcore) faunal heterogeneity increased markedly below the OMZ. Surface sediment pigment concentrations and oxygen together explained 96-99% of the variance in measures of E[S(100)], H' and J' across the transect; grain size and % TOC did not yield significant regressions. Pigments, assumed to reflect food availability and possibly oxygen effects on organic matter preservation, were negatively correlated with species richness and evenness, and positively correlated with dominance. The reverse was true for water depth. Macrobenthic patterns of calcification and lifestyle within the Oman margin OMZ (0.13-0.3 mi l(-1)) match the dysaerobic biofacies of paleo-environmental reconstruction models. (C) 1999 Elsevier Science Ltd. All rights reserved.

Levin, LA, Blair NE, Martin CM, Demaster DJ, Plaia G, Thomas CJ.  1999.  Macrofaunal processing of phytodetritus at two sites on the Carolina margin: in situ experiments using (13)C-labeled diatoms. Marine Ecology-Progress Series. 182:37-54.   10.3354/meps182037   AbstractWebsite

Tracer experiments using (13)C-labeled diatoms Thalassiosira pseudonana were carried out at two 850 m sites (I off Cape Fear and III off Cape Hatteras) on the North Carolina, USA, slope to examine patterns of macrofaunal consumption of fresh phytodetritus. Experiments examined the influence of taxon, feeding mode, body size and vertical position within the sediment column on access to surficial organic matter. delta(13)C measurements were made on macrofaunal metazoans and agglutinating protozoans from background sediments and from sediment plots in which (13)C-labeled diatoms were deposited and then sampled 0.3 h, 1 to 1.5 d, 3 mo and 14 mo later. Significant between-site differences were observed in background delta(13)C signatures of sediments, metazoans, and large, agglutinating protozoans, with values 2 to 3 parts per thousand lower at Site III than at Site I. Background delta(13)C signatures also varied as a function of taxon and of vertical position in the sediment column at Site III. The background delta(13)C value of carnivores was higher than that of surface-deposit feeders among Site I annelids, but no annelid feeding-group differences were observed at Site III. delta(13)C data from short-term (1 to 1.5 d) experiments revealed rapid diatom ingestion, primarily by agglutinated protozoans and annelids at Site I and mainly by annelids at Site III. Selective feeding on diatoms was exhibited by paraonid polychaetes, especially Aricidea spp. Exceptionally high uptake and retention of diatom C also was observed in the maldanid Praxillella sp., the nereid Ceratocephale sp. and several other surface-deposit feeding polychaetes. After 14 mo, little of the diatom (13)C remained at Site III, but high concentrations of the tracer were present in annelids and agglutinating protozoans at Site I. At both sites, nonannelid metazoans and subsurface-deposit feeding annelids exhibited the least uptake and retention of diatom C. Our hypotheses that large-bodied taxa and shallow-dwelling infauna should have greatest access to freshly deposited organic matter were not borne out. Some small, deep-dwelling taxa acquired label more readily than large or near-surface forms. Differences in tracer fates between sites reflected greater vertical mixing at Site III. These results indicate heterogeneity in benthic processes along the Carolina margin. but suggest that labile organic matter is consumed quickly at both sites. Because most of the taxa found to consume freshly deposited diatoms in these experiments are typical of bathyal settings, we infer that phytodetritus reaching the seabed in margin environments is rapidly processed by protozoan and metazoan components of the benthic fauna.