Spatial distribution of benthic foraminiferal stable isotopes and dinocyst assemblages in surface sediments of the Trondheimsfjord, central Norway

[摘要] Instrumental records from the Norwegian Sea and the Trondheimsfjord showevidence that changes of bottom water temperature and salinity in the fjordare linked to the salinity and temperature variability of the North AtlanticCurrent (NAC). Changes in primary productivity and salinity in the surfaceand intermediate water masses in the Trondheimsfjord as well as the fjordsedimentary budget are mainly driven by changes in riverine input. In thisstudy we use 59 surface sediment samples that are evenly distributed in thefjord to examine whether dinocyst assemblages and stable isotope ratios ofbenthic foraminifera reflect the present-day hydrology and can be used aspalaeoceanographic proxies. In general, modern benthic δ¹⁸O andδ¹³C values decrease from the fjord entrance towards the fjord headwith lowest values close to river inlets. This is essentially explained bygradients in the amounts of fresh water and terrigenous organic matterdelivered from the hinterland. The distribution of benthic δ¹³Cratios across the fjord is controlled by the origin (terrigenous vs. marine)of organic matter, local topography-induced variability in organic matterflux at the water–sediment interface, and organic matter degradation. Thedinocyst assemblages display the variations in hydrography with respect tothe prevailing currents, the topography, and the freshwater and nutrientsupply from rivers. The strength and depth of the pycnocline in the fjordstrongly vary seasonally and thereby affect water mass characteristics aswell as nutrient availability, temporally creating local conditions thatexplain the observed species distribution. Our results prove that dinocystassemblages and benthic foraminiferal isotopes reliably mirror the complexfjord hydrology and can be used as proxies of Holocene climatic variability.

[学科分类] 地球化学与岩石