• Energy Research

AbstractBuoyant freshwater released at depth from under Greenland's marine‐terminating glaciers gives rise to vigorous buoyant discharge plumes adjacent to the termini. The water mass found down fjord formed by mixing of buoyant subglacial freshwater and ambient fjord water and subsequent modification by glacial ice melt in the ice mélange is referred to as subglacial water. It substantially affects both the physical and chemical properties of the fjords' marine environment. Despite the importance of this freshwater source, many uncertainties remain regarding its transformation and detection. Here we present observations close to a marine‐terminating glacier in a fjord with substantial ice mélange and follow the down‐fjord changes of the subglacial discharge plume. Heat brought to the surface by entrainment of warm ambient fjord water into the rising plume causes intense melting of the ice mélange close to the plume pool. This results in an increase of glacial ice melt fraction to total glacial meltwater from 1–2% in the plume pool to ~18% eleven kilometers down‐fjord, with the largest increase being observed within the first few kilometers. Down‐fjord of the ice mélange two temperature minima bound the layer containing subglacial water. The upper bound is linked to the adjacent ice mélange and down‐fjord runoff sources, whereas the lower bound is linked to the stratification of the ambient water. We show that similar bounds can be observed in other marine‐terminating glacier fjords along West Greenland that contain an ice mélange, suggesting that similar processes work in other fjords.

Greenland's fjords and coastal waters are highly productive and sustain important fisheries. However, retreating glaciers and increasing meltwater are changing fjord circulation and biogeochemistry, which may threaten future productivity. The freshening of Greenland fjords caused by unprecedented melting of the Greenland Ice Sheet may alter carbonate chemistry in coastal waters, influencing CO2 uptake and causing biological consequences from acidification. However, few studies to date explore the current acidification state in Greenland coastal waters. Here we present the first-ever large-scale measurements of carbonate system parameters in 16 Greenlandic fjords and seek to identify the drivers of acidification state in these freshening ecosystems. Aragonite saturation state (Ω), a proxy for ocean acidification, was calculated from dissolved inorganic carbon (DIC) and total alkalinity from fjords along the east and west coast of Greenland spanning 68-75°N. Aragonite saturation was primarily >1 in the surface mixed layer. However, undersaturated-or corrosive--conditions (Ω < 1) were observed on both coasts (west: Ω = 0.28-3.11, east: Ω = 0.70-3.07), albeit at different depths. West Greenland fjords were largely corrosive at depth while undersaturation in East Greenland fjords was only observed in surface waters. This reflects a difference in the coastal boundary conditions and mechanisms driving acidification state. We suggest that advection of Sub Polar Mode Water and accumulation of DIC from organic matter decomposition drive corrosive conditions in the West, while freshwater alkalinity dilution drives acidification in the East. The presence of marine terminating glaciers also impacted local acidification states by influencing fjord circulation: upwelling driven by subglacial discharge brought corrosive bottom waters to shallower depths. Meanwhile, discharge from land terminating glaciers strengthened stratification and diluted alkalinity. Regardless of the drivers in each system, increasing freshwater discharge will likely lower carbonate saturation states and impact biotic and abiotic carbon uptake in the future.

The current downturn of the arctic cryosphere, such as the strong loss of sea ice, melting of ice sheets and glaciers, and permafrost thaw, affects the marine and terrestrial carbon cycles in numerous interconnected ways. Nonetheless, processes in the ocean and on land have been too often considered in isolation while it has become increasingly clear that the two environments are strongly connected: Sea ice decline is one of the main causes of the rapid warming of the Arctic, and the flow of carbon from rivers into the Arctic Ocean affects marine processes and the air-sea exchange of CO2. This review, therefore, provides an overview of the current state of knowledge of the arctic terrestrial and marine carbon cycle, connections in between, and how this complex system is affected by climate change and a declining cryosphere. Ultimately, better knowledge of biogeochemical processes combined with improved model representations of ocean-land interactions are essential to accurately predict the development of arctic ecosystems and associated climate feedbacks.

Abstract Hypoxic conditions (O 2 −1 ) are frequently observed in the relatively shallow and stratified North Sea–Baltic Sea transition zone. Inter-annual variability with more extensive hypoxia has been observed in years with calm weather conditions during late summer. A future warmer climate may increase hypoxia in the area due to combined effects from decreased oxygen solubility and increased respiration rates. Feedbacks from climate change can, therefore, amplify negative effects from eutrophication, such as hypoxia. Here we apply a high resolution three-dimensional ocean circulation model with a simple pelagic and benthic oxygen consumption model (OXYCON), based on the seasonal organic carbon budget in the area, and demonstrate that the model is able to simulate the temporal and spatial variability of the observed oxygen concentration in the bottom waters during a three-year period. The potential impact from a warmer climate was analysed in a sensitivity study with a 3 °C warmer climate, and showed a significant increase of hypoxic bottom areas compared to present day conditions. The relative role of increased respiration and decreased oxygen solubility in the inflowing bottom water and at the surface was analysed and it was found that decreased solubility accounted for about 25% of the simulated decrease in bottom water oxygen concentration in the centre of the area in the early fall. A sensitivity study showed that the simulated effect from a 3 °C temperature increase on the bottom water oxygen concentration could be compensated by a 30% reduction in the export production. The model simulations of the North Sea–Baltic Sea transition zone indicate a significant expansion of the hypoxic areas and a lengthening of the hypoxic period under a warmer climate.

Greenland’s fjords and coastal waters are highly productive and sustain important fisheries, but retreating glaciers and increasing meltwater supply are changing fjord circulation and biogeochemistry, which may threaten the future productivity of these unique ecosystems. The freshening of Greenland fjords caused by unprecedented melting of the Greenland Ice Sheet has the potential to alter carbonate chemistry in coastal waters, which would influence CO2 uptake as well as have biological consequences from acidification. However, few studies to date explore the current acidification state in Greenland coastal waters. Here we present the first-ever large-scale measurements of carbonate system parameters and δ18O measurements in 16 Greenlandic fjords and by combining datasets from two August cruises. HDMS Lauge Koch and RV Sanna cruises sampled on the East and West coast of Greenland in August 2018 and 2016 respectively. This dataset consists of 52 carbonate chemistry sample sites where dissolved inorganic carbon (DIC), total alkalinity (TA), and δ18O-H2O were measured throughout the water column. Water samples were collected in Niskin bottles and were transferred directly into triplicate 12 ml exetainers with a gas tight Tygon tubes, allowing overflow of at least 3 times the volume of the exetainer. Triplicate exetainers were collected for both DIC and TA at each depth. Samples were preserved with HgCl2 (saturated solution) to a final concentration of 0.02%. TA was measured on an Apollo SciTech AS-ALK2 total alkalinity titrator based on the Gran titration procedure for samples in West Greenland. While samples for East Greenland were measured on automatic titrator (Metrohm 888 Titrando), and a combined Metrohm glass electrode (Unitrode). DIC samples were analyzed on Apollo SciTech's AS-C3 analyzer for both cruises, using a sample volume of 0.5 ml. Routine analysis of Certified Reference Materials (provided by A. G. Dickson, Scripps Institution of Oceanography) verified that the accuracy of DIC and TA measurements. Coalescing this dataset therefore provides the first-ever analysis of wide-scale Greenland Fjord carbonate chemistry. Environmental variables recorded by CTD instruments are available for cruises from the West and East coasts respectively at the following DOIs: https://doi.org/10.5281/zenodo.4062024 and https://doi.org/10.5281/zenodo.5572329. We would like to thank the crew on board the HDMS Lauge Koch and RV Sanna for their collaboration. The Cruises were funded by Danish Centre for Marine Science (Grants: 2016-05 and 2017-06) and by the EU Horizon2020 funded project INTAROS (grant no. 727890) and the Danish Cooperation for Environment in the Arctic. This dataset is a contribution the project FACE-IT (The Future of Arctic Coastal Ecosystems – Identifying Transitions in Fjord Systems and Adjacent Coastal Areas). FACE-IT has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement no. 869154. Version 2 presents corrections in one file reporting DIC and TA data from Western Greenland. A systematic error was discovered in the labratory where the DIC samples were analyzed when converting from µmol L-1 to µmol kg-1. This error was corrected and the accurate values are now displayed in the file: SANNA_DIC_TA_corrected_2024.csv. Only the DIC values have changed. 

Abstract Data collected at open water stations (depth>400 m) in all major ocean basins in 2006–2008 are used to examine the relationship between the size structure of the phytoplankton community (determined by size fractionated chlorophyll filtration), temperature and inorganic nutrient availability. A significant relationship (p Laws et al., 2000 ) and integrated water column chlorophyll. Significant relationships were also found between mesozooplankton production (determined using the proxy of calanoid+cyclopoid nauplii abundance as a percentage of the total number of these copepods) and both temperature and phytoplankton size, with production being the lowest in the warmest waters where phytoplankton were the smallest. In the North Atlantic, export production and community size structure appear to be related to ocean uptake of CO2 from the atmosphere. The reported results suggest that ocean warming may directly alter plankton community structure. This, in turn, may alter the structure of marine food webs and impact the performance of the open ocean as a natural carbon sink.