Chytrid fungi distribution and co-occurrence with diatoms correlate with sea ice melt in the Arctic Ocean

Abstract. The Arctic Ocean gains freshwater mainly through river discharge, precipitation and the inflowing low salinity waters from the Pacific Ocean. In addition the recent reduction in sea ice volume is likely to influence the surface salinity and thus contribute to the freshwater content in the upper ocean. The present day freshwater storage in the Arctic Ocean appears to be sufficient to maintain the upper ocean stratification and to protect the sea ice from the deep ocean heat content. The recent freshening has not, despite the established strong stratification, been able to restrain the accelerating ice loss and other possible heat sources besides the Atlantic Water, such as the waters advecting from the Pacific Ocean and the solar insolation warming the Polar Mixed Layer, are investigated. Since the ongoing freshening, oceanic heat sources and the sea ice melt are closely related, this study, based on hydrographic observations, attempts to examine the ongoing variability in time and space in relation to these three properties. The largest time and space variability of freshwater content occurs in the Polar Mixed Layer and the upper halocline. The freshening of the upper ocean during the 2000s is ubiquitous in the Arctic Ocean although the most substantial increase occurs in the Canada Basin where the freshwater is accumulating in the thickening upper halocline. Whereas the salinity of the upper halocline is nearly constant, the freshwater content in the Polar Mixed Layer is increasing due to decreasing salinity. The decrease in salinity is likely to result from the recent changes in ice formation and melting. In contrast, in the Eurasian Basin where the seasonal ice melt has remained rather modest, the freshening of both the Polar Mixed Layer and the upper halocline is mainly of advective origin. While the warming of the Atlantic inflow was widespread in the Arctic Ocean during the 1990s, the warm and saline inflow events in the early 2000s appear to circulate mainly in the Nansen Basin. Nevertheless, even in the Nansen Basin the seasonal ice melt appears independent of the continuously increasing heat content in the Atlantic layer. As no other oceanic heat sources can be identified in the upper layers, it is likely that increased absorption of solar energy has been causing the ice melt prior to the observations.

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Arctic freshwater fluxes: sources, tracer budgets and inconsistencies

The Cryosphere ◽

10.5194/tc-13-2111-2019 ◽

2019 ◽

Vol 13 (8) ◽

pp. 2111-2131

Author(s):

Alexander Forryan ◽

Sheldon Bacon ◽

Takamasa Tsubouchi ◽

Sinhué Torres-Valdés ◽

Alberto C. Naveira Garabato

Keyword(s):

Sea Ice ◽

Arctic Ocean ◽

Inorganic Nutrients ◽

The Arctic ◽

Freshwater Flux ◽

Geochemical Tracers ◽

Ice Melt ◽

Boundary Velocity ◽

The Arctic Ocean ◽

Geochemical Method

Abstract. The net rate of freshwater input to the Arctic Ocean has been calculated in the past by two methods: directly, as the sum of precipitation, evaporation and runoff, an approach hindered by sparsity of measurements, and by the ice and ocean budget method, where the net surface freshwater flux within a defined boundary is calculated from the rate of dilution of salinity, comparing ocean inflows with ice and ocean outflows. Here a third method is introduced, the geochemical method, as a modification of the budget method. A standard approach uses geochemical tracers (salinity, oxygen isotopes, inorganic nutrients) to compute “source fractions” that quantify a water parcel's constituent proportions of seawater, freshwater of meteoric origin, and either sea ice melt or brine (from the freezing-out of sea ice). The geochemical method combines the source fractions with the boundary velocity field of the budget method to quantify the net flux derived from each source. Here it is shown that the geochemical method generates an Arctic Ocean surface freshwater flux, which is also the meteoric source flux, of 200±44 mSv (1 Sv=106 m3 s−1), statistically indistinguishable from the budget method's 187±44 mSv, so that two different approaches to surface freshwater flux calculation are reconciled. The freshwater export rate of sea ice (40±14 mSv) is similar to the brine export flux, due to the “freshwater deficit” left by the freezing-out of sea ice (60±50 mSv). Inorganic nutrients are used to define Atlantic and Pacific seawater categories, and the results show significant non-conservation, whereby Atlantic seawater is effectively “converted” into Pacific seawater. This is hypothesized to be a consequence of denitrification within the Arctic Ocean, a process likely becoming more important with seasonal sea ice retreat. While inorganic nutrients may now be delivering ambiguous results on seawater origins, they may prove useful to quantify the Arctic Ocean's net denitrification rate. End point degeneracy is also discussed: multiple property definitions that lie along the same “mixing line” generate confused results.

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Cyclone impact on sea ice in the central Arctic Ocean: a statistical study

The Cryosphere ◽

10.5194/tc-8-303-2014 ◽

2014 ◽

Vol 8 (1) ◽

pp. 303-317 ◽

Cited By ~ 15

Author(s):

A. Kriegsmann ◽

B. Brümmer

Keyword(s):

Sea Ice ◽

Arctic Ocean ◽

Ocean Model ◽

The Arctic ◽

Central Arctic Ocean ◽

Cumulative Impact ◽

Model Composite ◽

Ice Melt ◽

The Arctic Ocean ◽

The Impact

Abstract. This study investigates the impact of cyclones on the Arctic Ocean sea ice for the first time in a statistical manner. We apply the coupled ice–ocean model NAOSIM which is forced by the ECMWF analyses for the period 2006–2008. Cyclone position and radius detected in the ECMWF data are used to extract fields of wind, ice drift, and concentration from the ice–ocean model. Composite fields around the cyclone centre are calculated for different cyclone intensities, the four seasons, and different sub-regions of the Arctic Ocean. In total about 3500 cyclone events are analyzed. In general, cyclones reduce the ice concentration in the order of a few percent increasing towards the cyclone centre. This is confirmed by independent AMSR-E satellite data. The reduction increases with cyclone intensity and is most pronounced in summer and on the Siberian side of the Arctic Ocean. For the Arctic ice cover the cumulative impact of cyclones has climatologic consequences. In winter, the cyclone-induced openings refreeze so that the ice mass is increased. In summer, the openings remain open and the ice melt is accelerated via the positive albedo feedback. Strong summer storms on the Siberian side of the Arctic Ocean may have been important contributions to the recent ice extent minima in 2007 and 2012.

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Cyclone impact on sea ice in the central Arctic Ocean: a statistical study

The Cryosphere Discussions ◽

10.5194/tcd-7-1141-2013 ◽

2013 ◽

Vol 7 (2) ◽

pp. 1141-1176 ◽

Cited By ~ 3

Author(s):

A. Kriegsmann ◽

B. Brümmer

Keyword(s):

Sea Ice ◽

Arctic Ocean ◽

Ocean Model ◽

The Arctic ◽

Central Arctic Ocean ◽

Model Composite ◽

Ice Melt ◽

The Arctic Ocean ◽

Arctic Ice ◽

The Impact

Abstract. This study investigates the impact of cyclones on the Arctic Ocean sea ice for the first time in a statistical manner. We apply the coupled ice–ocean model NAOSIM which is forced by the ECMWF analyses for the period 2006–2008. Cyclone position and radius detected in the ECMWF data are used to extract fields of wind, ice drift, and concentration from the ice–ocean model. Composite fields around the cyclone centre are calculated for different cyclone intensities, the four seasons, and different regions of the Arctic Ocean. In total about 3500 cyclone events are analyzed. In general, cyclones reduce the ice concentration on the order of a few percent increasing towards the cyclone centre. This is confirmed by independent AMSR-E satellite data. The reduction increases with cyclone intensity and is most pronounced in summer and on the Siberian side of the Arctic Ocean. For the Arctic ice cover the impact of cyclones has climatologic consequences. In winter, the cyclone-induced openings refreeze so that the ice mass is increased. In summer, the openings remain open and the ice melt is accelerated via the positive albedo feedback. Strong summer storms on the Siberian side of the Arctic Ocean may have been important reasons for the recent ice extent minima in 2007 and 2012.

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Trends and spatial variation in rain-on-snow events over the Arctic Ocean during the early melt season

10.5194/tc-2020-214 ◽

2020 ◽

Author(s):

Tingfeng Dou ◽

Cunde Xiao ◽

Jiping Liu ◽

Qiang Wang ◽

Shifeng Pan ◽

...

Keyword(s):

Sea Ice ◽

Phase Change ◽

Arctic Ocean ◽

The Arctic ◽

Onset Date ◽

Marginal Seas ◽

Ice Melt ◽

The Pacific ◽

The Arctic Ocean ◽

Liquid Precipitation

Abstract. Rain-on-snow (ROS) events can accelerate the surface ablation of sea ice, thus greatly influencing the ice-albedo feedback. However, the variability of ROS events over the Arctic Ocean is poorly understood due to limited historical station data in this region. In this study early melt season ROS events were investigated based on four widely-used reanalysis products (ERA-Interim, JRA-55, MERRA2 and ERA5) in conjunction with available observations at Arctic coastal stations. The performance of the reanalysis products in representing the timing of ROS events and the phase change of precipitation was assessed. Our results show that ERA-Interim better represents the onset date of ROS events in spring and ERA5 better represents the phase change of precipitation associated with ROS events. All reanalyses indicate that ROS event timing has shifted to earlier dates in recent decades (with maximum trends up to −4 to −6 days/decade in some regions in ERA-Interim), and that sea ice melt onset in the Pacific sector and most of the Eurasian marginal seas is correlated with this shift. There has been a clear transition from solid to liquid precipitation, leading to more ROS events in spring, although large discrepancies were found between different reanalysis products. In ERA5, the shift from solid to liquid precipitation phase during the early melt season has directly contributed to a reduction in spring snow depth on sea ice by more than −0.5 cm/decade averaged over the Arctic Ocean since 1980, with the largest contribution (about −2.0 cm/decade) in the Kara-Barents Seas and Canadian Arctic Archipelago.

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Liquid export of Arctic freshwater components through the Fram Strait 1998–2011

Ocean Science ◽

10.5194/os-9-91-2013 ◽

2013 ◽

Vol 9 (1) ◽

pp. 91-109 ◽

Cited By ~ 34

Author(s):

B. Rabe ◽

P. A. Dodd ◽

E. Hansen ◽

E. Falck ◽

U. Schauer ◽

...

Keyword(s):

Sea Ice ◽

Arctic Ocean ◽

Meteoric Water ◽

The Arctic ◽

Ice Formation ◽

Fram Strait ◽

Pacific Water ◽

Ice Melt ◽

The North ◽

The Arctic Ocean

Abstract. We estimated the magnitude and composition of southward liquid freshwater transports in the East Greenland Current near 79° N in the Western Fram Strait between 1998 and 2011. Previous studies have found this region to be an important pathway for liquid freshwater export from the Arctic Ocean to the Nordic Seas and the North Atlantic subpolar gyre. Our transport estimates are based on six hydrographic surveys between June and September and concurrent data from moored current meters. We combined concentrations of liquid freshwater, meteoric water (river water and precipitation), sea ice melt and brine from sea ice formation, and Pacific Water, presented in Dodd et al. (2012), with volume transport estimates from an inverse model. The average of the monthly snapshots of southward liquid freshwater transports between 10.6° W and 4° E is 100 ± 23 mSv (3160 ± 730 km3 yr−1), relative to a salinity of 34.9. This liquid freshwater transport consists of about 130% water from rivers and precipitation (meteoric water), 30% freshwater from the Pacific, and −60% (freshwater deficit) due to a mixture of sea ice melt and brine from sea ice formation. Pacific Water transports showed the highest variation in time, effectively vanishing in some of the surveys. Comparison of our results to the literature indicates that this was due to atmospherically driven variability in the advection of Pacific Water along different pathways through the Arctic Ocean. Variations in most liquid freshwater component transports appear to have been most strongly influenced by changes in the advection of these water masses to the Fram Strait. However, the local dynamics represented by the volume transports influenced the liquid freshwater component transports in individual years, in particular those of sea ice melt and brine from sea ice formation. Our results show a similar ratio of the transports of meteoric water and net sea ice melt as previous studies. However, we observed a significant increase in this ratio between the surveys in 1998 and in 2009. This can be attributed to higher concentrations of sea ice melt in 2009 that may have been due to enhanced advection of freshwater from the Beaufort Gyre to the Fram Strait. Known trends and variability in the Arctic liquid freshwater inflow from rivers are not likely to have had a significant influence on the variation of liquid freshwater component transports between our surveys. On the other hand, known freshwater inflow variability from the Pacific could have caused some of the variation we observed in the Fram Strait. The apparent absence of a trend in southward liquid freshwater transports through the Fram Strait and recent evidence of an increase in liquid freshwater storage in the Arctic Ocean raise the question: how fast will the accumulated liquid freshwater be exported from the Arctic Ocean to the deep water formation regions in the North Atlantic and will an increased export occur through the Fram Strait.

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Trends and spatial variation in rain-on-snow events over the Arctic Ocean during the early melt season

The Cryosphere ◽

10.5194/tc-15-883-2021 ◽

2021 ◽

Vol 15 (2) ◽

pp. 883-895

Author(s):

Tingfeng Dou ◽

Cunde Xiao ◽

Jiping Liu ◽

Qiang Wang ◽

Shifeng Pan ◽

...

Keyword(s):

Sea Ice ◽

Phase Change ◽

Arctic Ocean ◽

The Arctic ◽

Onset Date ◽

Marginal Seas ◽

Ice Melt ◽

The Pacific ◽

The Arctic Ocean ◽

Liquid Precipitation

Abstract. Rain-on-snow (ROS) events can accelerate the surface ablation of sea ice, thus greatly influencing the ice–albedo feedback. However, the variability of ROS events over the Arctic Ocean is poorly understood due to limited historical station data in this region. In this study early melt season ROS events were investigated based on four widely used reanalysis products (ERA-Interim, JRA-55, MERRA, and ERA5) in conjunction with available observations at Arctic coastal stations. The performance of the reanalysis products in representing the timing of ROS events and the phase change of precipitation was assessed. Our results show that ERA-Interim better represents the onset date of ROS events in spring, and ERA5 better represents the phase change of precipitation associated with ROS events. All reanalyses indicate that ROS event timing has shifted to earlier dates in recent decades (with maximum trends up to −4 to −6 d per decade in some regions in ERA-Interim) and that sea ice melt onset in the Pacific sector and most of the Eurasian marginal seas is correlated with this shift. There has been a clear transition from solid to liquid precipitation, leading to more ROS events in spring, although large discrepancies were found between different reanalysis products. In ERA5, the shift from solid to liquid precipitation phase during the early melt season has directly contributed to a reduction in spring snow depth on sea ice by more than −0.5 cm per decade averaged over the Arctic Ocean since 1980, with the largest contribution (about −2.0 cm per decade) in the Kara–Barents seas and Canadian Arctic Archipelago.

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The impact of shallow stratification on air-sea CO2 flux in the summer Arctic Ocean

10.5194/egusphere-egu21-715 ◽

2021 ◽

Author(s):

Yuanxu Dong ◽

Dorothee Bakker ◽

Thomas Bell ◽

Peter Liss ◽

Ian Brown ◽

...

Keyword(s):

Surface Water ◽

Wind Speed ◽

Sea Ice ◽

Surface Temperature ◽

Arctic Ocean ◽

The Arctic ◽

Near Surface ◽

Ice Melt ◽

The Arctic Ocean ◽

The Impact

Air-sea carbon dioxide (CO2) flux is often indirectly estimated by the bulk method using the in-situ air-sea difference in CO2 fugacity and a wind speed dependent parameterisation of the gas transfer velocity (K). In the summer, sea-ice melt in the Arctic Ocean generates strong shallow stratification with significant gradients in temperature, salinity, dissolved inorganic carbon (DIC) and alkalinity (TA), and thus a near-surface CO2 fugacity &#160;(fCO2w) gradient. This gradient can cause an error in bulk air-sea CO2 flux estimates when the fCO2w is measured by the ship&#8217;s underway system at ~5 m depth. Direct air-sea CO2 flux measurement by eddy covariance (EC) is free from the impact of shallow stratification because the EC CO2 flux does not rely on a fCO2w measurement. In this study, we use summertime EC flux measurements from the Arctic Ocean to back-calculate the sea surface fCO2w and temperature and compare them with the underway measurements. We show that the EC air-sea CO2 flux agrees well with the bulk flux in areas less likely to be influenced by ice melt (salinity > 32). However, in regions with salinity less than 32, the underway fCO2w is higher than the EC estimate of surface fCO2w and thus the bulk estimate of ocean CO2 uptake is underestimated. The fCO2w difference can be partly explained by the surface to sub-surface temperature difference. The EC estimate of surface temperature is lower than the sub-surface water temperature and this difference is wind speed-dependent. Upper-ocean salinity gradients from CTD profiles suggest likely difference in DIC and TA concentrations between the surface and sub-surface water. These DIC and TA gradients likely explain much of the near-surface fCO2w gradient. Accelerating summertime loss of sea ice results in additional meltwater, which enhances near-surface stratification and increases the uncertainty of bulk air-sea CO2 flux estimates in polar regions.

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Evolution of the Arctic Ocean Salinity, 2007–08: Contrast between the Canadian and the Eurasian Basins

Journal of Climate ◽

10.1175/2010jcli3762.1 ◽

2011 ◽

Vol 24 (6) ◽

pp. 1705-1717 ◽

Cited By ~ 15

Author(s):

Camille Lique ◽

Gilles Garric ◽

Anne-Marie Treguier ◽

Bernard Barnier ◽

Nicolas Ferry ◽

...

Keyword(s):

Sea Ice ◽

Arctic Ocean ◽

The Arctic ◽

Global Ocean ◽

Fram Strait ◽

Atmospheric Conditions ◽

Ocean Reanalysis ◽

Sea Ice Extent ◽

Ice Melt ◽

The Arctic Ocean

Abstract The authors investigate the variability of salinity in the Arctic Ocean and in the Nordic and Labrador Seas over recent years to see how the freshwater balance in the Arctic and the exchanges with the North Atlantic have been affected by the recent important sea ice melting, especially during the 2007 sea ice extent minimum. The Global Ocean Reanalysis and Simulations (GLORYS1) global ocean reanalysis based on a global coupled ocean–sea ice model with an average of 12-km grid resolution in the Arctic Ocean is used in this regard. Although no sea ice data and no data under sea ice are assimilated, simulation over the 2001–09 period is shown to represent fairly well the 2007 sea ice event and the different components accounting for the ocean and sea ice freshwater budget, compared to available observations. In the reanalysis, the 2007 sea ice minimum is due to an increase of the sea ice export through Fram Strait (25%) and an important sea ice melt in the Arctic (75%). Liquid freshwater is accumulated in the Beaufort gyre after 2002, in agreement with recent observations, and it is shown that this accumulation is due to both the sea ice melt and a spatial redistribution of the freshwater content in the Canadian Basin. In the Eurasian Basin, a very contrasting situation is found with an increase of the salinity. The effect of the sea ice melt is counterbalanced by an increase of the Atlantic inflow and a modification of the circulation north of Fram Strait after 2007. The authors suggest that a strong anomaly of the atmospheric conditions was responsible for this change of the circulation.

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