@article {2615, title = {Microbial decomposition of marine dissolved organic matter in cool oceanic crust}, journal = {Nature Geoscience}, volume = {11}, year = {2018}, month = {Jan-05-2018}, pages = {334 - 339}, abstract = {Marine dissolved organic carbon (DOC) is one of the largest active reservoirs of reduced carbon on Earth. In the deep ocean, DOC has been described as biologically recalcitrant and has a radiocarbon age of 4,000 to 6,000 years, which far exceeds the timescale of ocean overturning. However, abiotic removal mechanisms cannot account for the full magnitude of deep-ocean DOC loss. Deep-ocean water circulates at low temperatures through volcanic crust on ridge flanks, but little is known about the associated biogeochemical processes and carbon cycling. Here we present analyses of DOC in fluids from two borehole observatories installed in crustal rocks west of the Mid-Atlantic Ridge, and show that deep-ocean DOC is removed from these cool circulating fluids. The removal mechanism is isotopically selective and causes a shift in specific features of molecular composition, consistent with microbe-mediated oxidation. We suggest organic molecules with an average radiocarbon age of 3,200 years are bioavailable to crustal microbes, and that this removal mechanism may account for at least 5\% of the global loss of DOC in the deep ocean. Cool crustal circulation probably contributes to maintaining the deep ocean as a reservoir of {\textquoteright}aged{\textquoteright} and refractory DOC by discharging the surviving organic carbon constituents that are molecularly degraded and depleted in C-14 and C-13 into the deep ocean.}, keywords = {carbon, community, deep-ocean, DISTINCT, extraction, fluid-flow, HEAT, MID-ATLANTIC RIDGE, SEAWATER, WESTERN FLANK}, issn = {1752-0894}, doi = {10.1038/s41561-018-0109-5}, url = {http://www.nature.com/articles/s41561-018-0109-5http://www.nature.com/articles/s41561-018-0109-5.pdfhttp://www.nature.com/articles/s41561-018-0109-5http://www.nature.com/articles/s41561-018-0109-5.pdf}, author = {Shah Walter, Sunita R. and Jaekel, Ulrike and Osterholz, Helena and Fisher, Andrew T. and Huber, Julie A. and Pearson, Ann and Dittmar, Thorsten and Girguis, Peter R.} } @article {2076, title = {Persistence of Gulf Stream separation during the Last Glacial Period: Implications for current separation theories}, journal = {Journal of Geophysical Research-Oceans}, volume = {108}, year = {2003}, note = {690nvTimes Cited:14 Cited References Count:56 }, month = {Jun 4}, abstract = {[1] We present stable oxygen isotope ratio (delta(18)O) measurements on deep-dwelling planktonic foraminifera from the western margin of the North Atlantic in order to reconstruct the latitude at which the Gulf Stream separated from the western boundary of the Atlantic Ocean in the past. The modern separation latitude can be reconstructed within one degree from delta(18)O measured on the fossil shells of deep-dwelling planktonic foraminifera Globorotalia truncatulinoides from the Holocene sediments representing the past 10,000 years of mild climate conditions similar to today. The separation latitude is captured in a sharp delta(18)O gradient, which reflects the prominent hydrographic change across the boundary between the warm waters south and east of the Gulf Stream and the cold Slope Water to the north. The latitudinal delta(18)O profile from approximately the Last Glacial Maximum shows that the Gulf Stream separated from the coast near Cape Hatteras at almost the same latitude as it does today. We assess our finding in light of existing Gulf Stream separation theories and conclude that one of the theories, the wind-induced separation mechanism, is not consistent with our paleoceanographic reconstruction.}, keywords = {cape-hatteras, deep-ocean, gulf stream separation, Last glacial maximum, marine sediment cores, north-atlantic, Ocean circulation, oxygen isotope composition, oxygen isotopic composition, past 21,000 years, planktonic foraminifera, planktonic-foraminifera, SARGASSO SEA, western boundary current, western boundary undercurrent, wind-driven}, isbn = {0148-0227}, doi = {10.1029/2001JC000861}, author = {Matsumoto, K. and Lynch-Stieglitz, J.} }