scholarly journals Relative sensitivity of the Atlantic meridional overturning circulation to river discharge into Hudson Bay and the Arctic Ocean

2007 ◽  
Vol 112 (G4) ◽  
pp. n/a-n/a ◽  
Author(s):  
Asa K. Rennermalm ◽  
Eric F. Wood ◽  
Andrew J. Weaver ◽  
Michael Eby ◽  
Stephen J. Déry
Keyword(s):  
Arctic Ocean ◽  
River Discharge ◽  
Relative Sensitivity ◽  
Atlantic Meridional Overturning Circulation ◽  
Meridional Overturning Circulation ◽  
The Arctic ◽  
Hudson Bay ◽  
Overturning Circulation ◽  
The Arctic Ocean ◽  
Meridional Overturning

scholarly journals Hydrological modelling of climate change impacts on river flows in Siberia's Lena River Basin and implications for the Atlantic Meridional Overturning Circulation

2019 ◽  
Vol 50 (6) ◽  
pp. 1577-1595 ◽  
Author(s):  
C. E. Hudson ◽  
J. R. Thompson
Keyword(s):  
River Basin ◽  
River Discharge ◽  
Atlantic Meridional Overturning Circulation ◽  
Meridional Overturning Circulation ◽  
The Arctic ◽  
Mean Annual Precipitation ◽  
Overturning Circulation ◽  
Lena River ◽  
Ensemble Mean ◽  
Meridional Overturning

Abstract A hydrological model of Siberia's Lena River Basin is calibrated and validated against observed river discharge at five stations. Implications of the Representative Concentration Pathway 4.5 scenario for river discharge are assessed using projections from 41 Coupled Model Intercomparison Project Phase 5 General Circulation Models grouped into 12 genealogical-based groups as well as a group ensemble mean. Annual precipitation increases in all scenarios (1.7–47.4%). Increases in annual PET are of a similar range (6.0–45.5%). PET peaks in June compared to July for the baseline. All temperature changes exceed 1.5 °C (range: 2.2 °C–6.2 °C). The largest absolute increases are in winter (maximum +7 °C). Changes in mean annual discharge range from −8.5 to +69.9%. Ten GCM groups and the group ensemble mean project increases. Earlier snowmelt is dominant so the annual flood peaks in May compared with June for the baseline. Increased discharge of the Lena and other Eurasian rivers to the Arctic Ocean has the potential to impact Atlantic Meridional Overturning Circulation (AMOC). Enhanced fluxes for four groups are capable of weakening the AMOC. Changes for other groups may contribute to weakening when combined with other sources of freshwater and warmer temperatures.

Impact of Arctic gateways closure on the Atlantic Meridional Overturning Circulation in the Pliocene

2021 ◽  
Author(s):  
Julia Weiffenbach ◽  
Michiel Baatsen ◽  
Anna von der Heydt
Keyword(s):  
Boundary Conditions ◽  
North Atlantic ◽  
Atlantic Meridional Overturning Circulation ◽  
Meridional Overturning Circulation ◽  
Sea Surface ◽  
The Arctic ◽  
Bering Strait ◽  
Overturning Circulation ◽  
The North ◽  
Meridional Overturning

<p>The mid-Pliocene climate is the most recent geological period with a greenhouse gas concentration of approximately 400 ppmv, similar to the present day. Proxy reconstructions indicate enhanced warming in the high North Atlantic in the mid-Pliocene, which has been suggested to be a response to a stronger Atlantic Meridional Overturning Circulation (AMOC). PlioMIP2 ensemble results show a stronger AMOC and simulated North Atlantic sea surface temperatures (SSTs) match reconstructions better than PlioMIP1. A major difference between PlioMIP1 and PlioMIP2 is the closure of the Bering Strait and Canadian Archipelago in the Pliocene. Previous studies have shown that closure of these Arctic gateways leads to an enhanced AMOC due to altered freshwater fluxes in the Arctic.</p><p>Analysis of our Community Earth System Model (CESM1) simulations shows that the simulated increase in North Atlantic SSTs and strengthened AMOC in the Pliocene is a result of Pliocene boundary conditions rather than CO<sub>2</sub> concentration increase. Here we compare results from two runs with pre-industrial boundary conditions and 280 and 560 ppmv CO<sub>2</sub> concentrations and three runs with PlioMIP2 boundary conditions and 280, 400 and 560 ppmv CO<sub>2</sub> concentrations. Results show a 10-15% stronger AMOC in the Pliocene simulations as well as enhanced warming and saltening of the North Atlantic sea surface. While there is a stronger AMOC, the Atlantic northward ocean heat transport (OHT) in the Pliocene simulations only increases 0-3% with respect to the pre-industrial. Analysis indicates there is an altered relationship between the AMOC and OHT in the Pliocene, pointing to fundamentally different behavior of the AMOC in the Pliocene simulations. This is supported by a specific spatial pattern of deep water formation (DWF) areas in the Pliocene simulations that is significantly different from that of the pre-industrial. In the Pliocene simulations, DWF areas adjacent to south Greenland disappear and new DWF areas appear further southwards in the Labrador Sea off the coast of Newfounland. These results indicate that insight into the effect of the palaeogeographic boundary conditions is crucial to understanding the Pliocene climate and its potential as a geological equivalent to a future greenhouse climate.</p>

The Effect of Arctic Freshwater Pathways on North Atlantic Convection and the Atlantic Meridional Overturning Circulation

2018 ◽  
Vol 31 (13) ◽  
pp. 5165-5188 ◽  
Author(s):  
He Wang ◽  
Sonya Legg ◽  
Robert Hallberg
Keyword(s):  
North Atlantic ◽  
Climate Models ◽  
Deep Convection ◽  
Atlantic Meridional Overturning Circulation ◽  
Meridional Overturning Circulation ◽  
The Arctic ◽  
Labrador Sea ◽  
Overturning Circulation ◽  
The North ◽  
Meridional Overturning

This study examines the relative roles of the Arctic freshwater exported via different pathways on deep convection in the North Atlantic and the Atlantic meridional overturning circulation (AMOC). Deep water feeding the lower branch of the AMOC is formed in several North Atlantic marginal seas, including the Labrador Sea, Irminger Sea, and the Nordic seas, where deep convection can potentially be inhibited by surface freshwater exported from the Arctic. The sensitivity of the AMOC and North Atlantic to two major freshwater pathways on either side of Greenland is studied using numerical experiments. Freshwater export is rerouted in global coupled climate models by blocking and expanding the channels along the two routes. The sensitivity experiments are performed in two sets of models (CM2G and CM2M) with different control simulation climatology for comparison. Freshwater via the route east of Greenland is found to have a larger direct impact on Labrador Sea convection. In response to the changes of freshwater route, North Atlantic convection outside of the Labrador Sea changes in the opposite sense to the Labrador Sea. The response of the AMOC is found to be sensitive to both the model formulation and mean-state climate.

A Diagnostic Indicator of the Stability of the Atlantic Meridional Overturning Circulation in CCSM3

2013 ◽  
Vol 26 (6) ◽  
pp. 1926-1938 ◽  
Author(s):  
Wei Liu ◽  
Zhengyu Liu
Keyword(s):  
Atlantic Meridional Overturning Circulation ◽  
Meridional Overturning Circulation ◽  
The Arctic ◽  
Overturning Circulation ◽  
Atlantic Basin ◽  
Climate System Model ◽  
Freshwater Transport ◽  
Meridional Overturning ◽  
The Stability ◽  
Diagnostic Indicator

Abstract A diagnostic indicator ΔMov is proposed in this paper to monitor the stability of the Atlantic meridional overturning circulation (AMOC). The ΔMov is a diagnostic for a basinwide salt-advection feedback and defined as the difference between the freshwater transport induced by the AMOC across the southern border of the Atlantic Ocean and the overturning liquid freshwater transport from the Arctic Ocean to the North Atlantic. As validated in the Community Climate System Model, version 3 (CCSM3), for an AMOC in the conveyor state, a positive ΔMov (freshwater convergence) in the Atlantic basin indicates a monostable AMOC and a negative ΔMov (freshwater divergence) indicates a bistable AMOC. Based on ΔMov, the authors investigate the AMOC stability in the Last Glacial Maximum (LGM) and analyze the modulation of the AMOC stability by an open/closed Bering Strait. Moreover, the authors estimate that the real AMOC is likely to be bistable in the present day, since some observations suggest a negative ΔMov (freshwater divergence) is currently in the Atlantic basin. However, this estimation is very sensitive to the choice of the observational data.

Sensitivity of the Atlantic Meridional Overturning Circulation to Model Resolution in CMIP6 HighResMIP Simulations

2020 ◽  
Author(s):  
Dorotea Iovino ◽  
Malcolm J. Roberts ◽  
Laura C. Jackson ◽  
Christopher D. Roberts ◽  
Virna Meccia ◽  
...  
Keyword(s):  
Heat Transport ◽  
Ocean Circulation ◽  
Atlantic Meridional Overturning Circulation ◽  
Meridional Overturning Circulation ◽  
The Arctic ◽  
Climate Modelling ◽  
Florida Current ◽  
Model Resolution ◽  
Overturning Circulation ◽  
Meridional Overturning

<p>The Atlantic Meridional Overturning Circulation (AMOC) is a key component of the three-dimensional ocean circulation that transports warm and salty water northward, and exports cold and dense water from the Arctic southward.</p><p>The simulated AMOC in Coupled Model Intercomparison Project models (both coupled and ocean-only) has been studied extensively. However, correctly simulating the AMOC with these models remains a challenge for the climate modelling community. One model aspect that can affect the AMOC representation is the model resolution (i.e. grid spacing).</p><p>Here, we examine key aspects of the North Atlantic Ocean circulation using a multi-model, multi-resolution ensemble based on the CMIP6 HighResMIP coupled experiments. The AMOC and associated heat transport tend to become stronger as model resolution increases, particularly when the ocean resolution changes from non-eddying to eddy-present and eddy-rich. However, the circulation remains too shallow compared to observations for most models, and this, together with temperature biases, cause the northward heat transport to be too low for a given overturning strength.</p><p>In the period 2015-2050, the overturning circulation tends to decline more rapidly in the higher resolution models by more than 20% compared to the control state, which is related to both themean state and to the subpolar gyre contribution to deep water formation. The main part of the decline comes from the Florida Current component of the circulation.</p>

scholarly journals Mechanisms Linking Volcanic Aerosols to the Atlantic Meridional Overturning Circulation

2012 ◽  
Vol 25 (8) ◽  
pp. 3039-3051 ◽  
Author(s):  
Alan M. Iwi ◽  
Leon Hermanson ◽  
Keith Haines ◽  
Rowan T. Sutton
Keyword(s):  
Volcanic Eruptions ◽  
Atlantic Meridional Overturning Circulation ◽  
Meridional Overturning Circulation ◽  
The Arctic ◽  
Similar Response ◽  
Overturning Circulation ◽  
Intergovernmental Panel ◽  
Western Atlantic ◽  
Meridional Overturning ◽  
Volcanic Aerosols

Abstract This study examines the sensitivity of the climate system to volcanic aerosol forcing in the third climate configuration of the Met Office Unified Model (HadCM3). The main test case was based on the 1880s when there were several volcanic eruptions, the well-known Krakatau being the largest. These eruptions increased atmospheric aerosol concentrations and induced a period of global cooling surface temperatures. In this study, an ensemble of HadCM3 has been integrated with the standard set of radiative forcings and aerosols from the Intergovernmental Panel on Climate Change Fourth Assessment Report simulations, from 1860 to present. A second ensemble removes the volcanic aerosols from 1880 to 1899. The all-forcings ensemble shows an attributable 1.2-Sv (1 Sv ≡ 106 m3 s−1) increase in the Atlantic meridional overturning circulation (AMOC) at 45°N—with a 0.04-PW increase in meridional heat transport at 40°N and increased northern Atlantic SSTs—starting around 1894, approximately 11 years after the first eruption, and lasting a further 10 years at least. The mechanisms responsible are traced to the Arctic, with suppression of the global water cycle (high-latitude precipitation), which leads to an increase in upper-level Arctic and Greenland Sea salinities. This then leads to increased convection in the Greenland–Iceland–Norwegian (GIN) Seas, enhanced Denmark Strait overflows, and AMOC changes with density anomalies traceable southward along the western Atlantic boundary. The authors investigate whether a similar response to the Pinatubo eruption in 1991 could still be ongoing, but do not find strong evidence.

Pliocene palaeoceanography of the Arctic Ocean and subarctic seas

2008 ◽  
Vol 367 (1886) ◽  
pp. 21-48 ◽  
Author(s):  
Jens Matthiessen ◽  
Jochen Knies ◽  
Christoph Vogt ◽  
Ruediger Stein
Keyword(s):  
Sea Ice ◽  
Arctic Ocean ◽  
Water Mass ◽  
Regional Scale ◽  
Meridional Overturning Circulation ◽  
The Arctic ◽  
Tectonic Activity ◽  
Major Influence ◽  
Overturning Circulation ◽  
The Arctic Ocean

The Pliocene is important in the geological evolution of the high northern latitudes. It marks the transition from restricted local- to extensive regional-scale glaciations on the circum-Arctic continents between 3.6 and 2.4 Ma. Since the Arctic Ocean is an almost land-locked basin, tectonic activity and sea-level fluctuations controlled the geometry of ocean gateways and continental drainage systems, and exerted a major influence on the formation of continental ice sheets, the distribution of river run-off, and the circulation and water mass characteristics in the Arctic Ocean. The effect of a water mass exchange restricted to the Bering and Fram Straits on the oceanography is unknown, but modelling experiments suggest that this must have influenced the Atlantic meridional overturning circulation. Cold conditions associated with perennial sea-ice cover might have prevailed in the central Arctic Ocean throughout the Pliocene, whereas colder periods alternated with warmer seasonally ice-free periods in the marginal areas. The most pronounced oceanographic change occurred in the Mid-Pliocene when the circulation through the Bering Strait reversed and low-salinity waters increasingly flowed from the North Pacific into the Arctic Ocean. The excess freshwater supply might have facilitated sea-ice formation and contributed to a decrease in the Atlantic overturning circulation.

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