Influence of Phytoplankton Advection on the Productivity Along the Atlantic Water Inflow to the Arctic Ocean

Abstract

Northwards flowing Atlantic waters transport heat, nutrients, and organic carbon in the form of zooplankton into the eastern Greenland Sea and Fram Strait. Less is known of the contribution of phytoplankton advection in this current, the Atlantic Water Inflow (AWI) spanning from the North Atlantic to the Arctic Ocean. The in situ and advected primary production was estimated using the physical-biological coupled SINMOD model over a region bounded by northern Norway coast (along the Norwegian Atlantic Current, NAC), the West Spitsbergen Current (WSC) and the entrance to the Arctic Ocean in northern Fram Strait. The simulation results show that changes in phytoplankton biomass at any one location along the AWI are supported primarily by advection. This advection is 5-50 times higher than the biomass photosynthesized in situ, seasonally variable, with minimum contribution in June, at the time of maximum in situ primary production. Advection in the NAC transports phytoplankton biomass from areas of higher production in the south, contributing to the maintenance of phytoplankton productivity further north. In situ productivity further decreases north of Svalbard Archipelago, at the entrance to the Arctic Ocean. Excess in situ annual production in northern WSC is exported to the Arctic Ocean during the growth season (April to September). The balance between in situ and advected primary production defines three main regions along the AWI, presumably modulated by the spatial and temporal variability of copepod grazing. As the sea ice reduces its annual extent and warmer waters enter the Arctic Ocean, ecological characteristics of the ice-free WSC with its AWI signature could extend north and east of Svalbard and into the central Arctic. Advection thus constitutes an important link connecting marine ecosystems of the Arctic and Atlantic Ocean, mainly at the gateways.

The influence of Arctic Fe and Atlantic fixed N on summertime primary production in Fram Strait, North Greenland Sea

“…No statistically significant responses to any of the supplied nutrient combinations relative to unamended controls were found in Experiments 3 and 4, located in the western and central Fram Straight respectively. This could either be a result of (i) limitation by an alternative resource (light or another nutrient); (ii) grazer regulation of the phytoplankton community, maintaining phytoplankton standing stocks despite enhanced specific growth rates following nutrient supply (e.g., Mann and Chisholm 64 ); or (iii) restricted net phytoplankton community growth over the experimental duration (72 h) due to low starting biomass concentrations and/or cold temperatures 65 . Our results do not allow us to unambiguously distinguish between these; however, ancillary observations allow identification of the most probable factors.…”

“…Additionally, some modelling suggests that decreasing sea-ice cover may lead to increased import of Atlantic Waters—and thus, fixed N—to the Fram Strait region 98 . Therefore in addition to changes in the areal extent of ice-free ocean 27 , 99 , 100 any future projection of primary production in the Fram Strait region is also hampered by poor knowledge of changes in nutrient supply as a result of the strong seasonal and inter-annual variability in current regimes 31 , 73 , changes in phytoplankton community composition and their nutrient requirements 57 , 65 , 101 . This compounds a poor mechanistic understanding of what drives elevated dFe and Si concentrations in the Transpolar Drift and how this will respond to future climate perturbations 19 , 45 , 75 .…”

Dynamics of organic matter and bacterial activity in the Fram Strait during summer and autumn

“…In the future, an increase in the amount of bioavailable DOM could stimulate the competition for mineral nutrients between phytoplankton and bacteria [90], releasing more CO 2 during bacterial respiration. Therefore, future changes to BP might reduce the net community production in the microbial food web and weaken CO 2 sequestration in the Arctic [27]. As such, parameters characterizing microbial food web dynamics, including components within semi-labile DOM, are of importance if we aim to assess future carbon cycling in the changing Arctic ecosystem.…”

Planktonic Protists of the Eastern Nordic Seas and the Fram Strait: Spatial Changes Related to Hydrography During Early Summer

“…Thus, it needs to be supplemented and validated with a significant amount of in situ observations. This is all the more important that the recent studies revealed potential climate-generated changes in the productivity of the Atlantic-Arctic sector, including slight trends toward higher productivity in the eastern Fram Strait (Nöthig et al, 2015), a considerable influence of AW advected phytoplankton on the local in situ primary production (Vernet et al, 2019), and a shift in the summer months plankton composition from large diatoms toward Phaeocystis pouchetii and other small flagellates (e.g., Lalande et al, 2013;Nöthig et al, 2015).…”