Publications

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2016
Burkett, AM, Rathburn AE, Perez ME, Levin LA, Martin JB.  2016.  Colonization of over a thousand Cibicidoides wuellerstorfi (foraminifera: Schwager, 1866) on artificial substrates in seep and adjacent off-seep locations in dysoxic, deep-sea environments. Deep-Sea Research Part I-Oceanographic Research Papers. 117:39-50.   10.1016/j.dsr.2016.08.011   AbstractWebsite

After-1 yr on the seafloor at water depths of similar to 700 m on Hydrate Ridge in the Pacific, eight colonization experiments composed primarily of a plastic mesh cube (from here on refered to as SEA(3), for Seafloor Epibenthic Attachment Cubes) were colonized by 1076 Cibicidoides wuellerstorfi on similar to 1841 cm(2) of experimental substrate. This species is typically considered an indicator of well-oxygenated conditions, and recruitment of such large numbers in bottom waters with low dissolved oxygen availability (0.24-0.37 mL/L) indicate that this taxon may not be as limited by oxygen as previously thought. Clues about substrate preferences were evident from the distribution, or lack thereof, of individuals among plastic mesh, coated steel frame, wooden dowels and reflective tape. Abundance, individual size distributions within cage populations and isotopic biogeochemistry of living foraminifera colonizing experimental substrates were compared between active seep and adjacent off seep experiment locations, revealing potential differences between these environments. Few studies have examined foraminiferal colonization of hard substrates in the deep-sea and to our knowledge no previous study has compared foraminiferal colonization of active seep and off-seep substrates from the same region. This study provides initial results of recruitment, colonization, geochemical and morphological aspects of the paleoceanographically significant species, C. wuellerstorfi, from dynamic deep-sea environments. Further experimental deployments of SEA(3)s will provide a means to assess relatively unknown ecologic dynamics of important foraminiferal deep-sea species.

2015
Maloney, JM, Grupe BM, Pasulka AL, Dawson KS, Case DH, Frieder CA, Levin LA, Driscoll NW.  2015.  Transpressional segment boundaries in strike-slip fault systems offshore southern California: Implications for fluid expulsion and cold seep habitats. Geophysical Research Letters. 42:4080-4088.   10.1002/2015gl063778   AbstractWebsite

The importance of tectonics and fluid flow in controlling cold seep habitats has long been appreciated at convergent margins but remains poorly understood in strike-slip systems. Here we present geophysical, geochemical, and biological data from an active methane seep offshore from Del Mar, California, in the inner California borderlands (ICB). The location of this seep appears controlled by localized transpression associated with a step in the San Diego Trough fault zone and provides an opportunity to examine the interplay between fluid expulsion and restraining step overs along strike-slip fault systems. These segment boundaries may have important controls on seep locations in the ICB and other margins characterized by strike-slip faulting (e.g., Greece, Sea of Marmara, and Caribbean). The strike-slip fault systems offshore southern California appear to have a limited distribution of seep sites compared to a wider distribution at convergent plate boundaries, which may influence seep habitat diversity and connectivity.

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.

2010
Baco, AR, Rowden AA, Levin LA, Smith CR, Bowden DA.  2010.  Initial characterization of cold seep faunal communities on the New Zealand Hikurangi margin. Marine Geology. 272:251-259.   10.1016/j.margeo.2009.06.015   AbstractWebsite

Cold-seep communities have been known from the North Atlantic and North Pacific for more than 20 years, but are only now being explored in the Southern Hemisphere While fisheries bycatch had suggested the presence of cold seeps on the New Zealand margin, the biodiversity and distribution of these communities remained unknown. Explorations using towed cameras and direct sampling gear revealed that cold seep sites are abundant along the New Zealand Hikurangi margin Initial characterization of the faunal communities at 8 of these sites indicates a fauna that is associated with particular sub-habitats but which varies in abundance between sites Community composition is typical, at higher taxonomic levels, of cold seep communities in other regions The dominant. symbiont-bearing taxa include siboglinid (tube) worms, vesicomyid clams and bathymodiolin mussels At the species level, much of the seep-associated fauna identified so far appears either to be new to science, or endemic to New Zealand seeps, suggesting the region may represent a new biogeographic province for cold-seep fauna Some overlap at the species and genus level is also indicated between the sampled seep communities and the fauna of hydrothermal vents on the Kermadec Arc in the region. Further taxonomic and genetic identifications of fauna from this study will allow us to fully test the levels of species overlap with other New Zealand chemosynthetic ecosystems as well as with other cold seep sites worldwide These apparently novel communities exhibit evidence of disturbance from a deep bottom-trawl fishery and appear to be threatened along the entire New Zealand margin. As bottom fisheries, mining, and fossil-fuel exploitation move into deeper waters, seep communities may be endangered worldwide, necessitating the initiation of conservation efforts even as new seep ecosystems are discovered and explored. Our findings highlight the unique nature of anthropogenic impacts in the deep-sea. in which reservoirs of biodiversity can be impacted long before they are even known. (C) 2009 Elsevier B V All rights reserved

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.

2003
Levin, LA, Ziebis W, Mendoza GF, Growney VA, Tryon MD, Brown KM, Mahn C, Gieskes JM, Rathburn AE.  2003.  Spatial heterogeneity of macrofauna at northern California methane seeps: influence of sulfide concentration and fluid flow. Marine Ecology-Progress Series. 265:123-139.   10.3354/meps265123   AbstractWebsite

Relationships among fluid flow, sulfide concentration, sulfur bacteria and macrofaunal assemblages were examined at methane seeps on the northern California margin, near the mouth of the Eel River (512 to 525 m). Over a 6 mo period, sediments covered with microbial mats exhibited significant but variable outflow of altered fluids, with no flow reversals. This fluid flow was associated with high porewater sulfide concentrations (up to 20 mM) and almost no oxygen penetration of sediments (<0.1 mm). Vesicomya pacifica (clam) bed and non-seep sediments exhibited little net fluid outflow and similar oxygen penetration (3 and 4 mm, respectively); however, sulfide concentrations were higher in subsurface clam-bed sediments (up to 2 mM) than in non-seep sediments (<200 muM). Macrofaunal densities did not differ among the 3 habitats (13 800 to 16 800 ind. m(-2); >300 mum), but biomass and diversity (no. species per core, E(S-100), H') were lower and composition varied in the sulfidic microbial mat sediments relative to clam-bed and non-seep sediments. The community in microbial mat-covered sediments consisted largely (82%) of 6 species in the polychaete family Dorvilleidae, whereas the clam-bed and non-seep microhabitats supported a mixture of annelids, peracarid crustaceans, nemerteans, and mollusks. Vertical microprofiling of sulfide in animal cores indicated that most taxa avoid H2S concentrations >1 mM. However, sulfide-oxidizing filamentous bacteria, dorvilleid polychaetes and bivalves (mainly V. pacifica) exhibited highest densities at sulfide concentrations of 1 to 5 mM sulfide. Horizontal and vertical patterns of sulfide availability have a strong influence on the fine-scale distribution, structure and composition of macrofaunal assemblages inhabiting methane seeps and must be accounted for when characterizing the microbiology and ecology of seep habitats.