Description: The research cruise M187 with the RV METEOR sailed January 25 th to March 4 th 2023 from Walvis Bay to Walvis Bay (Namibia), with a focus on investigating the biogeochemical gradients that exist between the Benguela Upwelling zone and the South Atlantic Subtropical Gyre. In order to achieve this, the two specific foci of the research cruise were to (i) track upwelling filaments as they advect offshore and interact with the subtropical gyre, and (ii) perform a high-resolution transect from upwelling sites to the subtropical gyre. On the research cruise, two filaments were successfully mapped from cold water upwelling sites near or over the Namibian shelf through to warmer waters offshore. This was followed by a transect of twelve stations outwards into the subtropical gyre, reaching a maximum westward position of 5 °W. Sampling stations were conducted to a maximum depth of 1000 m and involved an array of deployments to investigate the biogeochemistry of the water column. Further nutrient addition bioassay experiments were conducted throughout the research cruise to assess the nutrients (co-)limiting to phytoplankton growth. Collectively our research will shed light on key mechanisms establishing the major oceanic biogeochemical gradients between upwelling and subtropical gyre regions, so that they can be included in models used to predict the impacts of climate change.

Description: The Arctic Ocean is a region particularly prone to ongoing ocean acidification (OA) and climate-driven changes. The influence of these changes on Arctic phytoplankton assemblages, however, remains poorly understood. In order to understand how OA and enhanced irradiances (e.g., resulting from sea–ice retreat) will alter the species composition, primary production, and ecophysiology of Arctic phytoplankton, we conducted an incubation experiment with an assemblage from Baffin Bay (71°N, 68°W) under different carbonate chemistry and irradiance regimes. Seawater was collected from just below the deep Chl a maximum, and the resident pytoplankton were exposed to 380 and 1000 latm pCO2 at both 15 and 35% incident irradiance. On-deck incubations, in which temperatures were 6°C above in situ conditions, were monitored for phytoplankton growth, biomass stoichiometry, net primary production, photo-physiology, and taxonomic composition. During the 8-day experiment, taxonomic diversity decreased and the diatom Chaetoceros socialis became increasingly dominant irrespective of light or CO2 levels. We found no statistically significant effects from either higher CO2 or light on physiological properties of phytoplankton during the experiment. We did, however, observe an initial 2-day stress response in all treatments, and slight photo-physiological responses to higher CO2 and light during the first five days of the incubation. Our results thus indicate high resistance of Arctic phytoplankton to OA and enhanced irradiance levels, challenging the commonly predicted stimulatory effects of enhanced CO2 and light availability for primary production.

Description: The Arctic Ocean is one of the regions most prone to on-going ocean acidification (OA) and climate-driven changes, including increased sea surface temperature, sea-ice melt and altered mixing regimes. However, the influence of these changes on Arctic primary productivity, phytoplankton ecology and elemental cycles remains poorly understood. To date, the impact of various environmental stressors on phytoplankton have largely been assessed in isolation, and only limited process-understanding was gained. In order to understand how OA and enhanced irradiances (resulting from sea-ice retreat and increased mixed layer stratification) will alter the species composition, productivity and ecophysiology of Arctic phytoplankton, we conducted four incubation experiments with natural plankton assemblages from Davis Strait (63°N), Baffin Bay (71°N) and Kongsfjorden (Svalbard, 79°N). Phytoplankton assemblages were exposed to 400 and 1200 µatm pCO2 at both low and high irradiance levels over several weeks. These incubations were monitored and characterised in terms of phytoplankton growth, nutrient usage, biomass stoichiometry, net primary production (NPP), photophysiology and species composition. Preliminary results indicate that while the Subarctic Davis Strait assemblage exhibited light- and CO2-dependent growth rates and NPP, while there were no such differences between treatments in the Arctic assemblages (Baffin Bay and Svalbard). The observed similarities and differences in composition, productivity and physiology of phytoplankton assemblages grown under different climate scenarios will be discussed. Overall, our results indicate a high level of resilience of Arctic primary producers to climate-dependent environmental change.

Description: The Arctic Ocean is one of the regions most prone to on-going ocean acidification (OA) and climate-driven changes, including increased sea surface temperature, sea-ice melt and altered mixing regimes. However, the influence of these changes on Arctic primary productivity, phytoplankton ecology and elemental cycles remains poorly understood. To date, the impact of various environmental stressors on phytoplankton have largely been assessed in isolation, and only limited process-understanding was gained. In order to understand how OA and enhanced irradiances (resulting from sea-ice retreat and increased mixed layer stratification) will alter the species composition, productivity and ecophysiology of Arctic phytoplankton, we conducted two incubation experiments with natural plankton assemblages from Davis Strait (63°N) and Baffin Bay (71°N) during the Arctic-GEOTRACES summer 2015 campaign. Phytoplankton assemblages were exposed to 400 and 1200 µatm pCO2 at both 15% and 35% surface irradiance over two weeks. These incubations were monitored and characterised in terms of phytoplankton growth, nutrient usage, biomass stoichiometry, net primary production (NPP), photophysiology and species composition. Preliminary results indicate that the Subarctic Davis Strait assemblage exhibited light- and CO2-dependent growth rates and NPP, while there were no such differences between treatments in the Arctic Baffin Bay assemblage. The suite of physiological measurements conducted in this study will be exploited to provide a mechanistic understanding of the observed differences between phytoplankton assemblages. Results from our work will provide insight into the resilience of Arctic primary producers to climate-dependent environmental change.

Description: The Arctic Ocean is one of the regions most prone to on-going ocean acidification (OA) and climate-driven changes, including increased sea surface temperature, sea-ice melt and altered mixing regimes. However, the influence of these changes on Arctic primary productivity, phytoplankton ecology and elemental cycles remains poorly understood. To date, the impact of various environmental stressors on phytoplankton have largely been assessed in isolation, and only limited process-understanding was gained. In order to understand how OA and enhanced irradiances (resulting from sea-ice retreat and increased mixed layer stratification) will alter the species composition, productivity and ecophysiology of Arctic phytoplankton, we conducted two incubation experiments with natural plankton assemblages from Davis Strait (63°N) and Baffin Bay (71°N) during the Arctic-GEOTRACES summer 2015 campaign. Phytoplankton assemblages were exposed to 400 and 1200 µatm pCO2 at both 15% and 35% surface irradiance over two weeks. These incubations were monitored and characterised in terms of phytoplankton growth, nutrient usage, biomass stoichiometry, net primary production (NPP), photophysiology and species composition. Preliminary results indicate that the Subarctic Davis Strait assemblage exhibited light- and CO2-dependent growth rates and NPP, while there were no such differences between treatments in the Arctic Baffin Bay assemblage. The suite of measurements conducted in this study will be exploited to provide a mechanistic understanding of the observed similarities and differences between phytoplankton assemblages. Our results indicate a high level of resilience of Arctic primary producers to climate-dependent environmental change.

Description: The authors regret an error in the published article, where incorrect data was used to produce Figure 2, showing the temporal development of pH over the duration of the experiment. The corrected Fig. 2 shows that the error did not affect the interpretation of nor the conclusions drawn from the present dataset. The original article has been corrected.