The Structure of the Large-Scale Heliosphere as Seen by Current Models.

This review summarizes the current state of research aiming at a description of the global heliosphere using both analytical and numerical modeling efforts, particularly in view of the overall plasma/neutral flow and magnetic field structure, and its relation to energetic neutral atoms. Being part of a larger volume on current heliospheric research, it also lays out a number of key concepts and describes several classic, though still relevant early works on the topic. Regarding numerical simulations, emphasis is put on magnetohydrodynamic (MHD), multi-fluid, kinetic-MHD, and hybrid modeling frameworks. Finally, open issues relating to the physical relevance of so-called "croissant" models of the heliosphere, as well as the general (dis)agreement of model predictions with observations are highlighted and critically discussed

Tracing Glacial Meltwater From the Greenland Ice Sheet to the Ocean Using Gliders

The Greenland Ice Sheet (GrIS) is experiencing significant mass loss and freshwater discharge at glacier fronts. The freshwater input from Greenland will impact the physical properties of adjacent coastal seas, including important regions of deep water formation and contribute to global sea level rise. However, the biogeochemical impact of increasing freshwater discharge from the GrIS is less well constrained. Here, we demonstrate the use of bio-optical sensors on ocean gliders to track biogeochemical properties of meltwaters off southwest Greenland. Our results reveal that fresh, coastal waters, with an oxygen isotopic composition characteristic of glacial meltwater, are distinguished by a high optical backscatter and high levels of fluorescing dissolved organic matter (FDOM), representative of the overall colored dissolved organic matter pool. Reconstructions of geostrophic velocities are used to show that these particle and FDOM-enriched coastal waters cross the strong boundary currents into the Labrador Sea. Meltwater input into the Labrador Sea is likely driven by mesoscale processes, such as eddy formation and local bathymetric steering, in addition to wind-driven Ekman transport. Ocean gliders housing bio-optical sensors can provide the high-resolution observations of both dissolved and particulate glacially derived material that are needed to understand meltwater dispersal mechanisms and their sensitivity to future climatic change

The biogeochemical impact of glacial meltwater from Southwest Greenland

Biogeochemical cycling in high-latitude regions has a disproportionate impact on global nutrient budgets. Here, we introduce a holistic, multi-disciplinary framework for elucidating the influence of glacial meltwaters, shelf currents, and biological production on biogeochemical cycling in high-latitude continental margins, with a focus on the silica cycle. Our findings highlight the impact of significant glacial discharge on nutrient supply to shelf and slope waters, as well as surface and benthic production in these regions, over a range of timescales from days to thousands of years. Whilst biological uptake in fjords and strong diatom activity in coastal waters maintains low dissolved silicon concentrations in surface waters, we find important but spatially heterogeneous additions of particulates into the system, which are transported rapidly away from the shore. We expect the glacially-derived particles – together with biogenic silica tests – to be cycled rapidly through shallow sediments, resulting in a strong benthic flux of dissolved silicon. Entrainment of this benthic silicon into boundary currents may supply an important source of this key nutrient into the Labrador Sea, and is also likely to recirculate back into the deep fjords inshore. This study illustrates how geochemical and oceanographic analyses can be used together to probe further into modern nutrient cycling in this region, as well as the palaeoclimatological approaches to investigating changes in glacial meltwater discharge through time, especially during periods of rapid climatic change in the Late Quaternary

LADCP current data collected during RRS Discovery cruise DY081

This data release includes Lowered Acoustic Doppler Current Profile data collected during a 2017 (June - August) research expedition onboard the RRS Discovery, DY081, in the North Atlantic Ocean. DY081 was the first fieldwork component of a European Research Council funded project, ICY-LAB, led by Dr. K. Hendry from the University of Bristol to study nutrient cycling in the North Atlantic. Twenty-four CTD casts were carried out in four sites of interest: Orphan Knoll off the coast of Newfoundland, and Nuuk, Nasrsaq, and Cape Farewell off southwest Greenland. During each cast, two Teledyne RD WorkHorse 300 kHz ADCPs were secured to the CTD rosette facing in opposite directions. Raw LADCP data files were processed with the LDEO LADCP processing software version IX_8. The processing version was set to bottom tracking mode and employed auxiliary CTD time series data. Processed CTD profile files also incorporated GPS data stored parallel in time, arriving from the ship's 1 Hz feed. Pairing the CTD profile data with the LADCP casts in time is executed by correlating the pressure time series of the CTD file with the depth of the LADCP cast, itself calculated through integration of the vertical velocity. Shipboard ADCP data were not included in the processing procedure. Difficulties were encountered for the CTD stations near Nuuk in waters with a bottom depth shallower than 100m (station 11 and station 14), and with CTD station 22. See cruise report for full details. Note that no data were recorded from CTD station 12

Climate change and salinity of the coastal and marine environment around the UK

What is already happening • Salinity of eastern North Atlantic waters west of the UK has dramatically decreased over the last five years, probably in response to changes in the atmosphere in the western North Atlantic in the first years of the decade. • This dramatic freshening in ocean waters is not evident on the shelf beyond the northern North Sea waters east of Scotland with changes that appear within the bounds of typical interannual variability. • North of the UK, where the deep water (>800 m) flows from the Nordic Seas, the water freshened for five decades up until the late 1990s but has gradually become more saline over the last 20 years. • In the deep Rockall Trough where waters are thought to have originated in the North-West Atlantic, the salinity has remained stable over the last decade without the increases expected to have been passed on to it from changes in the Labrador Sea. • Some sustained observations are no longer available, but new models merged with data are just becoming available that may fill gaps in coverage. • Large interannual to decadal variability makes simple linear trends of salinity in the shelf seas less useful than assessments of identification of periods of fresh and saline anomalies. What could happen in the future? • There is considerable uncertainty regarding future salinity. • Most 21st Century projections suggest UK shelf seas, and the adjacent Atlantic Ocean, will be less saline than present, driven by ocean circulation changes in response to climate change. • Centennial-scale salinity decreases in UK shelf seas are likely to be driven by ocean circulation change. Reduced inflow across the ocean-to-shelf boundary is thought to be the main driver of the salinity decrease. • Greater salinity decreases are projected for the North Sea, than the Irish and Celtic Seas. Readers are referred to previous reports for MCCIP that have described the drivers, evidence base and decadal evolution of salinity in the seas around the UK (Gommenginger, 2006; Holliday et al., 2008, 2010; Dye et al., 2013). Here we update the time–series observations and describe how our knowledge has changed over the last five years

ICY-LAB DY081 Autonomous ocean glider data off Southwest Greenland

Two Slocum gliders (units 331 and 439) were deployed during RRS Discovery expedition DY081 on July 17th 2017 at 62.9°N, 52.6°W, approximately 40 km off the Greenland shelf break, travelled North along the coast in a zig-zag pattern between the shelf and deep waters, and were recovered 8 days later from 63.7°N, 53.1°W and 62.9° N, 52.7°W respectively on July 24th 2017. Gliders profiled from the surface to 1000 m, except during the two excursions onto the shelf, once south and once north of the Godthåb Trough, where they followed the bathymetry. Each glider was fitted with a pumped CTD and bio-optical sensors (WET Labs puck). These bio-optical sensors measure optical backscattering (in the form of volume scattering function), chlorophyll fluorescence, and UV fluorescence for fluorescing dissolved organic matter (FDOM), a subset of coloured organic matter (CDOM). This dataset contains raw and processed/gridded data files from the glider deployments. The raw data are contained as .dbd and .ebd files in ***_raw_data.zip folders for each of glider unit 331 and 439. The data were processed using the SOCIB glider toolbox (https://github.com/socib/glider_toolbox) and saved as a NetCDF (processed_***.nc) with the following variables: longitude, latitude, time (Julian Day), pressure, eastward velocity, northward velocity, temperature (not thermally corrected), salinity (not thermally corrected), chlorophyll fluorescence (not corrected for quenching), coloured organic matter (cdom), backscatter (volume scattering function) and oxygen concentration. The expedition report is provided and metadata can be found in the processed/gridded data files