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

Abstract

The Arctic Ocean is considerably affected by the consequences of global warming, including more extreme seasonal fluctuations in the physical environment. So far, little is known about seasonality in Arctic marine ecosystems in particular microbial dynamics and cycling of organic matter. The limited characterization can be partially attributed to logistic difficulties of sampling in the Arctic Ocean beyond the summer season. Here, we investigated the distribution and composition of dissolved organic matter (DOM), gel particles and heterotrophic bacterial activity in the Fram Strait during summer and autumn. Our results revealed that phytoplankton biomass influenced the concentration and composition of semi-labile dissolved organic carbon (DOC), which strongly decreased from summer to autumn. The seasonal decrease in bioavailability of DOM appeared to be the dominant control on bacterial abundance and activity, while no temperature effect was determined. Additionally, there were clear differences in transparent exopolymer particles (TEP) and Coomassie Blue stainable particles (CSP) dynamics. The amount of TEP and CSP decreased from summer to autumn, but CSP was relatively enriched in both seasons. Our study therewith indicates clear seasonal differences in the microbial cycling of organic matter in the Fram Strait. Our data may help to establish baseline knowledge about seasonal changes in microbial ecosystem dynamics to better assess the impact of environmental change in the warming Arctic Ocean. This article is part of the theme issue ‘The changing Arctic Ocean: consequences for biological communities, biogeochemical processes and ecosystem functioning’.

Spatio-Temporal Variations in Community Size Structure of Arctic Protist Plankton in the Fram Strait

“…Dotted lines indicate reduced reliability of size measurements for cells with ESD < 2 µm. For comparison, abundance and biovolume concentration densities derived from Flow Cytometry cell count measurements are shown for bacteria as horizontal lines (0.5-1.5 µm, assuming mean ESD = 1 µm, data from corresponding samples in von Jackowski et al (2020).…”

The changing Arctic Ocean: consequences for biological communities, biogeochemical processes and ecosystem functioning

“…Increased Atlantification in the region could contribute to prolonged uptake of atmospheric carbon in a warming Arctic. Von Jackowski et al [32] investigate bacterioplankton dynamics that are affected by changes in the organic matter pool. They show that seasonal patterns in pelagic primary production affect availability of dissolved organic matter (DOM), and the availability of substrate has a greater impact on bacterial activity than increasing temperature.…”

The Polar Night Shift: Annual Dynamics and Drivers of Microbial Community Structure in the Arctic Ocean

“…Our study is embedded in the long-term HAUSGARTEN and FRAM observatories studying primary productivity, benthopelagic coupling and deep-sea ecology since the 1990s 31,32 . The recent deployment of autonomous devices provides a key advance to characterize complete annual cycles, expanding on summertime snapshots of microbial diversity, biogeography and activity [33][34][35][36][37][38][39] . Annual records are also important to understand biological responses to the northward expansion of subarctic habitats, often coined Atlantification, which propagates through the entire food web 40,41 .…”