Abundance and production rates of heterotrophic bacterioplankton in the context of sediment and water column processes in the Chukchi Sea

Abstract

Bacterial production and abundance are linked to areas of high biological production in the water column and in the underlying benthos in the Chukchi Sea. Process measurements taken during the Russian American Long-term Census of the Arctic (RUSALCA) program, such as the carbon isotope composition of sinking particulate organic matter and sediment organic matter, are used to put bacterial production and abundance in context. These measurements show that there are vertical gradients in the water column and that the stable carbon isotope composition of organic materials in the sediments is significantly different from sedimenting materials in the overlying water column. Differences within the water column likely reflect late summer declines in productivity that increase discrimination against 13C and also provide indications of carbon metabolism in the water column and underlying sediments. Temporal changes in the stable carbon isotope composition of organic matter in surface sediments, as well as C/N ratios in organic matter during the RUSALCA program, are also being observed, specifically higher ratios of 13C/12C at some stations near the Chukotka coast, and lower ratios of 13C/12C near Point Hope, Alaska. C/N ratios have increased since 2004 at productive sites in the south central Chukchi Sea, suggesting changes in organic material deposition. Other parameters studied on some or all of the decadal series of joint Russia-US cruises include sediment oxygen demand, the nitrogen isotopic composition of organic matter, sediment grain size, chlorophyll content in surface sediments, and elemental ratios of carbon and nitrogen in surface sediments. These process measurements support interpretations that the ecosystem shows strong coupling between bacterial and primary production and the underlying benthos.