Search

The international and interdisciplinary sea-ice drift expedition “The Multidisciplinary drifting Observatory for the Study of Arctic Climate” (MOSAiC) was conducted from October 2019 to September 2020. The aim of MOSAiC was to study the interconnected physical, chemical, and biological characteristics and processes from the atmosphere to the deep sea of the central Arctic system. The ecosystem team addressed current knowledge gaps and explored unknown biological properties over a complete seasonal cycle focusing on three major research areas: biodiversity, biogeochemical cycles, and linkages to the environment. In addition to the measurements of core properties along a complete seasonal cycle, dedicated projects covered specific processes and habitats, or organisms on higher taxonomic or temporal resolution in specific time windows. A wide range of sampling instruments and approaches, including sea-ice coring, lead sampling with pumps, rosette-based water sampling, plankton nets, remotely operated vehicles, and acoustic buoys, was applied to address the science objectives. Further, a broad range of process-related measurements to address, for example, productivity patterns, seasonal migrations, and diversity shifts, were made both in situ and onboard RV Polarstern. This article provides a detailed overview of the sampling approaches used to address the three main science objectives. It highlights the core sampling program and provides examples of habitat- or process-specific sampling. The initial results presented include high biological activities in wintertime and the discovery of biological hotspots in underexplored habitats. The unique interconnectivity of the coordinated sampling efforts also revealed insights into cross-disciplinary interactions like the impact of biota on Arctic cloud formation. This overview further presents both lessons learned from conducting such a demanding field campaign and an outlook on spin-off projects to be conducted over the next

The ocean biological carbon pump (BCP) plays a pivotal role in the global carbon cycle. The BCP magnitude is determined by the fraction of nutrients utilised in biological production and remineralised at depth, with the remainder being subducted into the interior unused as ‘preformed’ nutrients. This fraction is currently around 50% and subject to the interaction of biological processes and global scale circulation. Consequently, changes in circulation can potentially impact biological carbon storage. Here we provide observational evidence that the reduction in the Atlantic Meridional Overturning Circulation (AMOC) that occurred over the 2004-2018 period has been accompanied by substantial changes in nutrient transports and associated carbon storage. Persistent southward net nutrient transport across 26.5°N exceeded nutrient sources, except by the end of the period when the system approached balance. This transient net loss of nutrients from the North Atlantic was accompanied by increases in the ratio of remineralized to preformed nutrients, indicating an increasing BCP efficiency (and carbon storage). Our results thus demonstrate observable transient changes in large scale nutrient transports linked to AMOC changes over interannual - decadal timescales, with implications for future ocean carbon storage.

Arctic Ocean properties and processes are highly relevant to the regional and global coupled climate system, yet still scarcely observed, especially in winter. Team OCEAN conducted a full year of physical oceanography observations as part of the Multidisciplinary drifting Observatory for the Study of the Arctic Climate (MOSAiC), a drift with the Arctic sea ice from October 2019 to September 2020. An international team designed and implemented the program to characterize the Arctic Ocean system in unprecedented detail, from the seafloor to the air-sea ice-ocean interface, from sub-mesoscales to pan-Arctic. The oceanographic measurements were coordinated with the other teams to explore the ocean physics and linkages to the climate and ecosystem. This paper introduces the major components of the physical oceanography program and complements the other team overviews of the MOSAiC observational program. Team OCEAN’s sampling strategy was designed around hydrographic ship-, ice- and autonomous platform-based measurements to improve the understanding of regional circulation and mixing processes. Measurements were carried out both routinely, with a regular schedule, and in response to storms or opening leads. Here we present alongdrift time series of hydrographic properties, allowing insights into the seasonal and regional evolution of the water column from winter in the Laptev Sea to early summer in Fram Strait: freshening of the surface, deepening of the mixed layer, increase in temperature and salinity of the Atlantic Water. We also highlight the presence of Canada Basin deep water intrusions and a surface meltwater layer in leads. MOSAiC most likely was the most comprehensive program ever conducted over the ice-covered Arctic Ocean. While data analysis and interpretation are ongoing, the acquired datasets will support a wide range of physical oceanography and multi-disciplinary research. They will provide a significant foundation for assessing and advancing modeling cap

Unprecedented quantities of heat are entering the Pacific sector of the Arctic Ocean through Bering Strait, particularly during summer months. Though some heat is lost to the atmosphere during autumn cooling, a significant fraction of the incoming warm, salty water subducts (dives beneath) below a cooler fresher layer of near-surface water, subsequently extending hundreds of kilometers into the Beaufort Gyre. Upward turbulent mixing of these sub-surface pockets of heat is likely accelerating sea ice melt in the region. This Pacific-origin water brings both heat and unique biogeochemical properties, contributing to a changing Arctic ecosystem. However, our ability to understand or forecast the role of this incoming water mass has been hampered by lack of understanding of the physical processes controlling subduction and evolution of this this warm water. Crucially, the processes seen here occur at small horizontal scales not resolved by regional forecast models or climate simulations; new parameterizations must be developed that accurately represent the physics. Here we present novel high resolution observations showing the detailed process of subduction and initial evolution of warm Pacific-origin water in the southern Beaufort Gyre.

Unprecedented quantities of heat are entering the Pacific sector of the Arctic Ocean through Bering Strait, particularly during summer months. Though some heat is lost to the atmosphere during autumn cooling, a significant fraction of the incoming warm, salty water subducts (dives beneath) below a cooler fresher layer of near-surface water, subsequently extending hundreds of kilometers into the Beaufort Gyre. Upward turbulent mixing of these sub-surface pockets of heat is likely accelerating sea ice melt in the region. This Pacific-origin water brings both heat and unique biogeochemical properties, contributing to a changing Arctic ecosystem. However, our ability to understand or forecast the role of this incoming water mass has been hampered by lack of understanding of the physical processes controlling subduction and evolution of this this warm water. Crucially, the processes seen here occur at small horizontal scales not resolved by regional forecast models or climate simulations; new parameterizations must be developed that accurately represent the physics. Here we present novel high resolution observations showing the detailed process of subduction and initial evolution of warm Pacific-origin water in the southern Beaufort Gyre.

Unprecedented quantities of heat are entering the Pacific sector of the Arctic Ocean through Bering Strait, particularly during summer months. Though some heat is lost to the atmosphere during autumn cooling, a significant fraction of the incoming warm, salty water subducts (dives beneath) below a cooler fresher layer of near-surface water, subsequently extending hundreds of kilometers into the Beaufort Gyre. Upward turbulent mixing of these sub-surface pockets of heat is likely accelerating sea ice melt in the region. This Pacific-origin water brings both heat and unique biogeochemical properties, contributing to a changing Arctic ecosystem. However, our ability to understand or forecast the role of this incoming water mass has been hampered by lack of understanding of the physical processes controlling subduction and evolution of this this warm water. Crucially, the processes seen here occur at small horizontal scales not resolved by regional forecast models or climate simulations; new parameterizations must be developed that accurately represent the physics. Here we present novel high resolution observations showing the detailed process of subduction and initial evolution of warm Pacific-origin water in the southern Beaufort Gyre.

The Arctic Ocean is particularly sensitive to climate change. Its ecosystem structure and function are prone to be disturbed by fast warming and massive retreat of sea-ice, which in turn, might result in feedbacks on climate. Moreover, such drastic changes are expected to influence the meridional fluxes of heat, freshwater and biogeochemical tracers between subpolar areas and the Arctic. As the third most important greenhouse gas and major ozone-depleting substance in the stratosphere, nitrous oxide (N2O) is a crucial gas to study in order to assess the ocean’s role in the production and exchange of climate-relevant compounds to the atmosphere. Between 2018 and 2019 we conducted ship-based surveys to elucidate the source-sink dynamics of N2O in the subpolar-polar North Atlantic. Based on results from those campaigns, we show the distribution and spatial variability of surface N2O, which ranged from moderate supersaturation (positive sea-air fluxes) in ice-free subpolar areas to unusually strong undersaturation (negative sea-air fluxes) in partially or fully ice-covered areas. We also present a comprehensive overview of the water column distribution of N2O in the region, and by combining this data with hydrographic and chemical (O2 and inorganic nutrients) information, we trace back the origin of the dominant water masses so as to illustrate the connectivity between the Fram Strait and the Nordic Seas off southeast Greenland. This analysis is used to discuss how the meridional water mass exchange in the region influences the balance of local vs. remote N2O production and its spatial variability. Furthermore, we use the results from collocated molecular analyses (functional gene markers) to infer the occurrence and abundances of the main microbial communities responsible for the cycling of N2O. This contribution is relevant for assessments of expected changes in trace gas emissions with further climate-driven changes in the Arctic Ocean.

Global climate is critically sensitive to physical and biogeochemical dynamics in the subpolar Southern Ocean, since itnis here that deep, carbon-rich layers of the world ocean outcrop and exchange carbon with the atmosphere. Here, we present evidence that the conventional framework for the subpolar Southern Ocean carbon cycle, which attributes a dominant role to the vertical overturning circulation and shelf-sea processes, fundamentally misrepresents the drivers of regional carbon uptake. Observations in the Weddell Gyre —a key representative region of the subpolar Southern Ocean— show that the rate of carbon uptake is set by an interplay between the Gyre’s horizontal circulation and the remineralization at mid-depths of organic carbon sourced from biological production in the central gyre. These results demonstrate that reframing the carbon cycle of the subpolar Southern Ocean is an essential step to better define its role in past and future climate change.

The Arctic Ocean is undergoing remarkable environmental changes due to global warming. The rise in the Arctic near-surface air temperature during the past decades is twice as high as the global average, a phenomenon known as the “Arctic Amplification”. As a consequence the Arctic summer sea ice extent has decreased by more than 40 % in recent decades, and moreover a year-round sea ice loss in extent and thickness was recorded. By opening up of large areas formerly covered by sea ice, the exchange of heat, moisture and momentum between the ocean and atmosphere intensified. This resulted in changes in the ocean circulation and the water masses impacting the marine ecosystem. We investigate these changes by using a large set of hydrographic and biogeochemical data of the entire Arctic Ocean. To better quantify the current changes in the Arctic ecosystem we will combine our observational data analysis with model simulations using a very high resolution (1/12°) biogeochemical atmosphere-sea ice-ocean model from our partners at the National Oceanographic Center in the UK (Yevgeni Aksenov and Stefanie Rynders).

Stable isotope tracer incubation techniques were used to estimate the uptake of nitrogen by phytoplankton growth in the Southampton Water estuarine system over the productive spring-summer period in 2001 and 2002. Nutrient uptake experiments were carried out at approximately 2 week intervals with water samples collected from three stations in the estuary, representative of coastal waters of the Solent, the mid-estuary and brackish waters of the system. In 2001, separate subsamples were incubated with 13C-HCO3 and 15N-NO3-, 15N-NH+4, and 15N-urea, and were deployed in situ at 4 photic depths plus a dark incubation. In 2002, separated subsamples were incubated with 15N-NO-3 and 15N-NH4+, and were deployed at 2 photic depths. In addition, in 2002 the release of DON and the regeneration of NH4+ were also quantified. Vertical profiles of temperature, salinity and irradiance were made at each station, and water samples from 5 depths were collected for later analysis of nutrients (nitrate, ammonium, urea, and silicate) and chlorophyll a. Chlorophyll a concentrations of up to 64 μg L-1 were measured, and generally increased from the coastal waters towards the upper estuary. Nutrient concentration were also higher in the inner estuary and appear to be affected by the seasonal cycle of phytoplankton growth, showing lower concentrations during the summer months. Uptake rates of nitrogen within the Southampton Water estuary were comparable with value reported in the literature for other similar estuaries and coastal systems, and showed that during extensive phytoplankton blooms within these systems comparatively elevated uptake rates can be reached. In general, the temporal variation in the uptake of N-nutrients was consistent with the seaso