Predicting sediment organic carbon and related food web types from a physical oceanographic model on a subarctic shelf- South of St. Lawrence Island, 2006-2007

In changing environments, conservation planning for bottom-feeding marine predators requires estimating the present and future spatial patterns of benthic communities. In the northern Bering Sea, we used the Regional Ocean Modeling System (ROMS) to hindcast near-bottom flows that redistribute settled phytodetritus and organic sediments, which in turn strongly affect the dispersion of three food web types that differentially favor spectacled eiders Somateria fischeri, walruses Odobenus rosmarus, or gray whales Eschrichtius robustus. Using data collected between 1994 and 2010, we interpolated spatial patterns of sediment organic carbon from field samples and correlated them with water depths and modeled flow velocities, temperatures, and salinities. In the deeper (mean 63 meters) southern study area with weak net flows, hindcast near-bottom currents had negligible effects on patterns of sediment longer-term organic carbon (LTOC); instead, regional depth gradients and local bathymetry were the best predictors (r 2 = 0.72–0.85 among 7 years). In that area, climatic variations in total primary production would affect the areal extent of different LTOC levels, but not the core locations of persistent patches defined by depth. In the shallower (mean 39 meters) northern study area with much faster flows, seafloor depth had negligible effects and patterns of LTOC depended mainly on currents (r 2 = 0.48–0.55 over 2 years) that are subject to climatic changes in winds. Based on ranges of LTOC for different food web types, substantial portions of both areas must be conserved to ensure annual availability of all three types. Regional ocean circulation models driven by downscaled climate models provide important opportunities for projecting spatial patterns of key benthic habitats in this region.在不断变化的环境中，针对底栖觅食海洋捕食者的保护规划，需要估算底栖生物群落当前与未来的空间分布格局。在白令海北部海域，我们采用区域海洋模式系统（Regional Ocean Modeling System, ROMS）对近底流场进行后报，该流场会重新分布沉降的浮游生物碎屑与有机沉积物，进而显著影响三类食物网类型的分布——这三类食物网分别偏好斑头海番鸭（*Somateria fischeri*）、海象（*Odobenus rosmarus*）与灰鲸（*Eschrichtius robustus*）。我们利用1994年至2010年间采集的野外样本数据，对沉积物有机碳的空间分布格局进行插值，并将其与水深、模式模拟得到的流速、温度及盐度进行相关性分析。在平均水深63米、净流较弱的南部研究区，后报得到的近底流场对沉积物长期有机碳（long-term organic carbon, LTOC）的分布格局影响可忽略不计；取而代之的是，区域水深梯度与局地测深地形为最佳预测因子（7个年份的r²为0.72~0.85）。在该区域，总初级生产力的气候波动会改变不同LTOC等级的分布范围，但不会改变由水深界定的持久性斑块的核心位置。在平均水深39米、流场流速更快的北部研究区，海底水深对LTOC分布格局的影响可忽略不计，其分布主要受流场控制（2个年份的r²为0.48~0.55），而流场变化受风力的气候波动影响。基于不同食物网类型对应的LTOC阈值范围，需对两个研究区的大片区域开展保护，以确保三类食物网每年均可获得充足的资源供给。由降尺度气候模式驱动的区域海洋环流模式，为该区域关键底栖生境的空间分布格局预测提供了重要途径。