95 research outputs found
Historical (1985-2015) Fram Strait volume, heat, and salt transports in CMIP6 models
No full textThis Dataset contains Fram Strait volume, heat, and salt transport calculations for one ensemble member of each of 13 climate models participating in the Coupled Model Intercomparison Project phase 6 (CMIP6). The 13 models are BCC-CSM2-MR, CAMS-CSM1-0, CanESM5, CESM2, EC-Earth3, GFDL-CM4, GISS-E2-1-H, IPSL-CM6A-LR, MIROC6, MPI-ESM1-2-HR, MRI-ESM2-0, NorESM2-LM, and UKESM1-0-LL. For each model, transports are provided along a depth vs longitude section at monthly resolution over years 1985-2015 of the CMIP6 historical simulation. All transports are provided on the models' native grids except for GISS-E2-1-H and NorESM2-LM. The data are stored in netcdf format with metadata in each file including the variant label of the ensemble member and model-specific constants used for the transport calculations
Atlantic Water in the Arctic Ocean - Mechanisms and Impacts
Full text linkThe Arctic Ocean plays a fundamental role in regulating Earth’s climate, and a changing Arctic will affect climate, weather, and life everywhere on the planet. Understanding the fundamental dynamics and mechanisms driving natural variability, and the effects of anthropogenic warming in the Arctic climate system is imperative to improve future climate predictions. Warm and saline Atlantic Water (AW) entering the region across the Greenland-Scotland Ridge is the primary heat source to the Arctic Ocean and plays an essential role in modulating the Arctic climate system. However, our knowledge is still insufficient to make skillful projections of future Arctic climate change with uncertainty levels similar to other regions. This thesis improves our understanding of the role of AW in the Arctic Ocean, focusing primarily on: its variations in the twentieth and twenty-first centuries; the underlying mechanisms governing this variability; and its proliferating regional impacts on sea ice, marine-terminating glaciers, and stratification.
First, we investigate the twentieth-century variability of AW heat transport through the gates of the Arctic Ocean. The analysis is based on a simulation from the global ocean-ice Norwegian Earth System Model (NorESM) supported by an extensive set of hydrographic observations dating back to 1900. We quantify prominent variability in both AW temperature and volume transport on near-decadal time scales, as well as significant positive trends in the most recent decades. Variations in volume transport were found to be linked to the wind forcing in the Nordic Seas and Subtropical North Atlantic, as manifested through the North Atlantic Oscillation, although the correlation is not constant over time and breaks down entirely in specific periods, such as the Early Twentieth Century Warming period. Variations in temperature are a combination of advected signals originating upstream and variations in atmospheric cooling over the Nordic Seas, which effectively dampen the AW heat anomalies along their path northward.
Secondly, we provide a further in-depth investigation of the relationship between the AW flow and wind forcing. Here, we analyze results from a coordinated wind perturbation experiment in a suite of nine different Arctic Ocean models, and calculate “Climate Response Functions” (CRFs) to isolate the effects of wind anomalies on AW circulation, sea ice, and hydrography. The CRFs show that anomalously strong/weak wind forcing over the Greenland Sea results in an intensification/weakening of the poleward AW flow and a reduction/increase in the Arctic sea ice cover. Despite biases in hydrograph, all models respond in a similar manner to the anomalous winds and show a near-linear relationship between AW volume and heat transport, surface heat loss, and sea ice extent in the Barents Sea. Historical reconstructions show that the largescale wind forcing alone can explain 50% of the AW flow variance, indicating potential for predictability.
Third, we focus on the export of meltwater from Upernavik Fjord in northwest Greenland as the combined result of melting caused by AW and the release of subglacial discharge at the fronts of marine-terminating glaciers. Using hydrographic observations collected between 2013 and 2019 we provide the first description of the hydrographic structure in Upernavik Fjord, explain the complex water mass transformation occurring in the fjord, and quantify the composition of the water mass exported from the fjord. We show that meltwater is heavily diluted and exported as “Glacially Modified Water” (GMW), which in summer is composed of 57.8 +/-8.1% AW, 41.0 +/-8.3% Polar Water, 1.0 +/-0.1% subglacial discharge, and 0.2 +/-0.2% submarine meltwater. Consistent with its composition, we show a close relationship between water mass properties on the continental shelf (AW and Polar Water) and the exported GMW properties, and estimate an exchange across the fjord mouth of 50 mSv. This study provides a first order parameterization for the exchange at the mouth of glacial fjords for large-scale ocean models.
Finally, we investigate changes in central Arctic Ocean stratification in the twentieth and twenty-first centuries. Observations show that from 1970 to 2017, the stratification in the Amerasian Basin has strengthened, whereas the stratification has weakened in parts of the Eurasian Basin. These contrasting results are due to competing effects of increasing AW influence (“Atlantification) and local freshening. Simulations from the Community Earth System Model Large Ensemble and a suite of nine CMIP6 models project that under a strong greenhouse-gas forcing scenario (RCP8.5/SSP585), the upper layers in the Amerasian Basin will become even more stratified in the future. In the Eurasian Basin, models show diverging results, with approximately half of the models projecting a strengthened stratification in the future and the other half projecting a weakened stratification. These differences are mainly a result of different balances between local processes and advected signals.
Combined, the four papers highlight the diverse yet significant role of AW in the Arctic environment and advance our knowledge of the broad-scale mechanisms governing AW variability and the impacts of AW on different components of the climate system. Our results provide a spatially and temporally inclusive progressed understanding of natural and anthropogenic climate change in the Arctic and ultimately contribute to improved projections of future Arctic climate change.Doktorgradsavhandlin
Matlab code for the paper "Future sea ice weakening amplifies wind-driven trends in surface stress and Arctic Ocean spin-up"
No full text<p>Matlab code used to process data for the paper "Future sea ice weakening amplifies wind-driven trends in surface stress and Arctic Ocean spin-up". </p>
Temperature and Salinity profiles from Upernavik Fjord, Northwest Greenland, from 2013 to 2019
No full textBottom melting of Arctic Sea Ice in the Nansen Basin due to Atlantic Water influence
Full text linkThe hydrographic situation for a region north of Svalbard is investigated using observations from the Norwegian Young Sea Ice Cruise (N-ICE2015). Observations from January to June 2015 are compared to historical observations with a particular focus on the warm and salty Atlantic Water (AW) entering the Arctic Ocean through the Fram Strait. Here we discuss how the AW has changed over time, what governs its characteristics, and how it might influence the sea ice cover. We find that AW characteristics north of Svalbard are mainly controlled by the distance along the inflow path, and by changes in inflowing AW temperature in the Fram Strait. AW characteristics north of Svalbard are also largely affected by local processes such as sea ice growth, melting and tidal induced mixing. Furthermore, one dimensional model results and observations show that AW has a direct impact on the sea ice cover north of Svalbard. Shallow and warm AW efficiently reduces sea ice growth and results in bottom melting throughout the whole year. The historical observations and outcome from a fully coupled earth system model show a warming trend of AW core temperature over the last few decades. We believe that the AW warming trend in the Arctic Ocean may be part of long term multi-decadal variability, which is influenced by anthropogenic forcing. Simulations suggest that approximately 30 % of the recent warming may be attributed to global warming
Vertical profiles of temperature and salinity in the Central Arctic Ocean from observations and 13 CMIP6 models - 1970-2017
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The Eurasian Arctic Ocean along the MOSAiC drift (2019-2020): Core hydrographic parameters
No full textThe Eurasian Arctic Ocean along the MOSAiC drift (2019-2020): Core hydrographic parameters
No full textThe Eurasian Arctic Ocean along the MOSAiC drift (2019-2020): Core hydrographic parameters
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