Fluxes of Sedimentary Material in the Lofoten Basin of the Norwegian Sea: Seasonal Dynamics and the Role of Zooplankton

Abstract

We studied sedimentation processes in the Lofoten Basin of the Norwegian Sea based on data of the Automatic Deep-Sea Sedimentation Observatory (ADSO) deployed for a year (August 2017–July 2018). The article presents estimates of the vertical fluxes of total sedimentary material, organic carbon (Corg), calcium carbonate (CaCO3), biogenic silica (SiO2bio), aluminum, and the particles of planktonic origin (pteropods, foraminifera, fecal pellets, necrozooplankton). The seasonal pattern of total vertical flux is characterized by a unimodal distribution with a maximum in September 2017 (191 mg dry weight m–2 day–1) in the 0–500 m surface water layer. The total flux decreases markedly from November and reaches the minimum (2.6 mg m–2 day–1) in March–April 2018. The maximum Corg flux values (5.2 mg C m–2 day–1), CaCO3 (178 mg CaCO3 m–2 day–1), and SiO2bio (9.1 mg SiO2bio m–2 day–1) are observed in autumn. The value of fluxes and the portion of lithogenic material in it are higher at a depth of 2950 m due to redeposition from the nepheloid layer. The amplitude of flux variations during the year is noticeably smaller at this depth. The highest fluxes are related to the maass sedimentation of juvenile pteropods Limacina retroversa. The contribution of pteropods to vertical fluxes in autumn is 60–100% for CaCO3 and 56–73% for Corg. The contribution of foraminifera to the total CaCO3 flux does not exceed 6% and only reaches 60% at a depth of 550 m in October. The flux of fecal pellets, where ostracod pellets dominate, varies from <0.01 to 2.1 mgC m–2 day–1, making up from 0.1 to 90% of the Corg flux. The flux of zooplankton carcasses (ZCs) in the 0–550 m water layer varies from 0 to 0.45 mgC m–2 day–1, reaching the maximum value in February. The share of ZCs flux was 0–33% in the summer–autumn season, 12–52% in winter, and 23–41% in spring relative to the total (taking into account the ZCs) Corg flux. The ZCs flux varied from 0.04 to 0.22 mgC m–2 day–1 in the near-bottom water layer and amounted to 0.7–2% of the total Corg flux. The total contribution of all studied planktonic particles to the annual CaCO3 flux was 16–47%, and their contribution to the annual Corg flux was 37–45%. Comparative analysis of our results and published data obtained in the 1990s demonstrates that the observed climatic changes (increasing temperature and salinity, as well as an increase in the thickness of the Atlantic water layer) in the Lofoten Basin did not result in significant changes in the quantitative characteristics of sedimentation process.