Impact of Amur riverine discharge on sediment composition, primary producitvity and nutrient utilization in the Okhotsk Sea
Abstract
The Okhotsk Sea is governed by exceptional climatic conditions, amongst which are the southernmost extent of sea-ice within the world ocean and high, mostly biosiliceous, productivity turning this marginal sea into a major sink for CO2 within the North Pacific realm. In addition, a notably variable discharge by the river Amur transports large amounts of freshwater and detritus into the basin. The depositional environment in the western Okhotsk Sea is predominantly characterized by three constituents: firstly, the delivery of Ice-Rafted Debris (IRD) via sea ice transport, secondly high primary productivity produces biogenic opal dispersed to the sea floor. Finally, large portions of terrigenous-siliciclastic and organic matter enter the investigated area by the discharge of the Amur. Our intention is to reconstruct the impact of freshwater discharge on the sedimentary and oceanographic settings and the interplay with rapid natural climatic changes in late Pleistocene-Holocene. To facilitate this prospectus, we investigated recent boundary conditions for sediment deposition. We use Multicorer sediment surface samples along the continental margin of Sakhalin, following the main pathway of the Amur freshwater flow. Additional sediment surface samples from other areas like Derugin Basin, the Central Okhotsk Sea and Kamchatka continental margin endorse our dataset and serve as reference for open ocean conditions and intra-basin gradients within our proxies. We use accumulation rates and contents of biogenic opal, TOC/TC, nitrogen, C/N and N-15 isotope ratios as well as distribution of chlorophycean algae as proxies for spatial distribution of freshwater discharge, biogenic productivity and nutrient utilization processes. Our proxy-dataset correlates well with the main flow characteristics of riverine freshwater along the continental margin of E-Sakhalin. However, along Sakhalin and some deeper parts of the Derugin Basin, additional supply of terrestrial organic matter also plays a crucial role in the development of thick annual phytodetritus layers and the development of oxygen minimum zones or even suboxic conditions in the past. Finally, intercomparison of our varied records permits to evaluate the significance and soundness of previous datasets and helps to test proxies so far unused in this region against well-established records.
- Publication:
-
EGS - AGU - EUG Joint Assembly
- Pub Date:
- April 2003
- Bibcode:
- 2003EAEJA....11878L