Estimating global warming and natural variability signals in the ocean south of Iceland

2020 ◽  
Author(s):  
Steingrímur Jónsson
Keyword(s):  
Global Warming ◽  
Ocean Circulation ◽  
Water Mass ◽  
Marine Species ◽  
Atlantic Multidecadal Oscillation ◽  
Natural Variability ◽  
Tropical Water ◽  
Relative Contribution ◽  
Mass Properties ◽  
Lower Temperature

<p>The temperature in the Atlantic waters south of Iceland has increased by about 1°C since 1995 with most of the rise occurring before 2000. A similar rise in air temperature in Iceland was observed simultaneously and the rise in temperature is often interpreted as being caused by global warming. Many effects of this in the ocean and on land such as changed distribution of marine species in the area as well as melting of glaciers in Iceland have been attributed to this rising temperature. However, it is unlikely that this rapid increase in temperature was solely due to global warming, especially since it was accompanied by an increase in salinity. It is more likely that there was a change in the ocean circulation in the area leading to more sub-tropical water entering the sub-polar gyre causing a shift in temperature and salinity. A similar increase in temperature and salinity was observed earlier during 1930-1964 in this area. Between the two warm periods the waters were dominated by lower temperature and salinity. These changes have been related to the Atlantic Multidecadal Oscillation. By comparing the water mass properties in the two warm periods it is possible to estimate the relative contribution from natural variability and global warming for the recent warm period. It will be shown how the retreat and advancing of glaciers in Iceland are in harmony with the changes in water mass properties in the waters south of Iceland. It is important that decisions about how to adapt to coming climate change are based on how much of the observed change is due to natural variability and global warming respectively. This is a method that can be used in other areas of the northern North Atlantic.</p>

Moored Observations of Currents and Water Mass Properties between Talaud and Halmahera Islands at the Entrance of the Indonesian Seas

2021 ◽  
Vol 51 (12) ◽  
pp. 3557-3572
Keyword(s):  
Water Mass ◽  
Low Frequency ◽  
Maximum Velocity ◽  
Boreal Winter ◽  
Indonesian Seas ◽  
Seasonal Movement ◽  
Tropical Water ◽  
The Pacific ◽  
Mass Properties ◽  
Channel Velocity

AbstractThe currents and water mass properties at the Pacific entrance of the Indonesian seas are studied using measurements of three subsurface moorings deployed between the Talaud and Halmahera Islands. The moored current meter data show northeastward mean currents toward the Pacific Ocean in the upper 400 m during the nearly 2-yr mooring period, with the maximum velocity in the northern part of the channel. The mean transport between 60- and 300-m depths is estimated to be 10.1–13.2 Sv (1 Sv ≡ 106 m3 s−1) during 2016–17, when all three moorings have measurements. The variability of the along-channel velocity is dominated by low-frequency signals (periods > 150 days), with northeastward variations in boreal winter and southwestward variations in summer in the superposition of the annual and semiannual harmonics. The current variations evidence the seasonal movement of the Mindanao Current retroflection, which is supported by satellite sea level and ocean color data, showing a cyclonic intrusion into the northern Maluku Sea in boreal winter whereas a leaping path occurs north of the Talaud Islands in summer. During Apri–July, the moored CTDs near 200 m show southwestward currents carrying the salty South Pacific Tropical Water into the Maluku Sea.

scholarly journals Eddy-Induced Variability in a Transatlantic Section: Argo Observing System–Gyroscope 0302 Cruise Comparison

2005 ◽  
Vol 22 (7) ◽  
pp. 1069-1079
Author(s):  
Manuel Vargas-Yáñez ◽  
Gregorio Parrilla ◽  
Alicia Lavín ◽  
Pedro Vélez-Belchí ◽  
César González-Pola ◽  
...  
Keyword(s):  
Real Time ◽  
Ocean Circulation ◽  
Time Scale ◽  
Spatial Interpolation ◽  
Sampling Design ◽  
Water Mass ◽  
Time Variability ◽  
Regular Grid ◽  
Mass Properties ◽  
Zonal Section

Abstract Ocean hydrological sections provide a very useful mean to study the ocean circulation as well as to determine water mass properties and to estimate fluxes. One basic method for their analysis is the spatial interpolation of data, obtained from a set of predefined stations, into a regular grid for contouring isolines and for further calculations. The shortest length scales that can be solved are limited by the distance between stations. Some of these scales, though resoluble by the sampling design, may be, with respect to time variability, shorter than the time that is needed to complete the section. This situation can produce a lack of synopticity in the obtained data, which is not usually addressed in oceanographic studies because the sequential repetition of oceanographic surveys is not an easy task. Here two samplings are compared—one by CTD- and another by Array for Real-Time Geostrophic Oceanography (Argo)-type profilers—of the same zonal section with a 5-day delay. The integral time scale for the mesoscale field is around 11 days, which implies that the mesoscale signal obtained from consecutive transmissions of the profilers are weakly correlated. The mesoscale field in a transatlantic section, which typically takes 20 days to be carried out, cannot be considered as synoptic.

scholarly journals 2 °C vs. High Warming: Transitions to Flood-Generating Mechanisms across Canada

Water ◽  
2021 ◽  
Vol 13 (11) ◽  
pp. 1494
Author(s):  
Bernardo Teufel ◽  
Laxmi Sushama
Keyword(s):  
Climate Change ◽  
Global Warming ◽  
Climate Model ◽  
Regional Climate ◽  
Adaptation Measures ◽  
Relative Contribution ◽  
Late 21St Century ◽  
Transient Climate Change ◽  
Projected Changes ◽  
Change Mitigation

Fluvial flooding in Canada is often snowmelt-driven, thus occurs mostly in spring, and has caused billions of dollars in damage in the past decade alone. In a warmer climate, increasing rainfall and changing snowmelt rates could lead to significant shifts in flood-generating mechanisms. Here, projected changes to flood-generating mechanisms in terms of the relative contribution of snowmelt and rainfall are assessed across Canada, based on an ensemble of transient climate change simulations performed using a state-of-the-art regional climate model. Changes to flood-generating mechanisms are assessed for both a late 21st century, high warming (i.e., Representative Concentration Pathway 8.5) scenario, and in a 2 °C global warming context. Under 2 °C of global warming, the relative contribution of snowmelt and rainfall to streamflow peaks is projected to remain close to that of the current climate, despite slightly increased rainfall contribution. In contrast, a high warming scenario leads to widespread increases in rainfall contribution and the emergence of hotspots of change in currently snowmelt-dominated regions across Canada. In addition, several regions in southern Canada would be projected to become rainfall dominated. These contrasting projections highlight the importance of climate change mitigation, as remaining below the 2 °C global warming threshold can avoid large changes over most regions, implying a low likelihood that expensive flood adaptation measures would be necessary.

scholarly journals Global heat balance and heat uptake in potential temperature coordinates

2021 ◽  
Author(s):  
Antoine Hochet ◽  
Rémi Tailleux ◽  
Till Kuhlbrodt ◽  
David Ferreira
Keyword(s):  
Global Warming ◽  
Water Mass ◽  
Potential Temperature ◽  
Effective Diffusion ◽  
Mitigation Strategies ◽  
Ocean Heat Uptake ◽  
Cold Temperatures ◽  
Advection Diffusion Equation ◽  
Advection Diffusion ◽  
Heat Uptake

AbstractThe representation of ocean heat uptake in Simple Climate Models used for policy advice on climate change mitigation strategies is often based on variants of the one-dimensional Vertical Advection/Diffusion equation (VAD) for some averaged form of potential temperature. In such models, the effective advection and turbulent diffusion are usually tuned to emulate the behaviour of a given target climate model. However, because the statistical nature of such a “behavioural” calibration usually obscures the exact dependence of the effective diffusion and advection on the actual physical processes responsible for ocean heat uptake, it is difficult to understand its limitations and how to go about improving VADs. This paper proposes a physical calibration of the VAD that aims to provide explicit traceability of effective diffusion and advection to the processes responsible for ocean heat uptake. This construction relies on the coarse-graining of the full three-dimensional advection diffusion for potential temperature using potential temperature coordinates. The main advantage of this formulation is that the temporal evolution of the reference temperature profile is entirely due to the competition between effective diffusivity that is always positive definite, and the water mass transformation taking place at the surface, as in classical water mass analyses literature. These quantities are evaluated in numerical simulations of present day climate and global warming experiments. In this framework, the heat uptake in the global warming experiment is attributed to the increase of surface heat flux at low latitudes, its decrease at high latitudes and to the redistribution of heat toward cold temperatures made by diffusive flux.

scholarly journals Relative timing of precipitation and ocean circulation changes in the western equatorial Atlantic over the last 45 kyr

2018 ◽  
Vol 14 (9) ◽  
pp. 1315-1330 ◽  
Author(s):  
Claire Waelbroeck ◽  
Sylvain Pichat ◽  
Evelyn Böhm ◽  
Bryan C. Lougheed ◽  
Davide Faranda ◽  
...  
Keyword(s):  
Mass Transport ◽  
Ocean Circulation ◽  
North Atlantic ◽  
Wavelet Transforms ◽  
Water Mass ◽  
Sediment Cores ◽  
Equatorial Atlantic ◽  
The North ◽  
Atmospheric Changes ◽  
Circulation Changes

Abstract. Thanks to its optimal location on the northern Brazilian margin, core MD09-3257 records both ocean circulation and atmospheric changes. The latter occur locally in the form of increased rainfall on the adjacent continent during the cold intervals recorded in Greenland ice and northern North Atlantic sediment cores (i.e., Greenland stadials). These rainfall events are recorded in MD09-3257 as peaks in ln(Ti ∕ Ca). New sedimentary Pa ∕ Th data indicate that mid-depth western equatorial water mass transport decreased during all of the Greenland stadials of the last 40 kyr. Using cross-wavelet transforms and spectrogram analysis, we assess the relative phase between the MD09-3257 sedimentary Pa ∕ Th and ln(Ti ∕ Ca) signals. We show that decreased water mass transport between a depth of ∼1300 and 2300 m in the western equatorial Atlantic preceded increased rainfall over the adjacent continent by 120 to 400 yr at Dansgaard–Oeschger (D–O) frequencies, and by 280 to 980 yr at Heinrich-like frequencies. We suggest that the large lead of ocean circulation changes with respect to changes in tropical South American precipitation at Heinrich-like frequencies is related to the effect of a positive feedback involving iceberg discharges in the North Atlantic. In contrast, the absence of widespread ice rafted detrital layers in North Atlantic cores during D–O stadials supports the hypothesis that a feedback such as this was not triggered in the case of D–O stadials, with circulation slowdowns and subsequent changes remaining more limited during D–O stadials than Heinrich stadials.

scholarly journals Ocean Convection

Fluids ◽  
2021 ◽  
Vol 6 (10) ◽  
pp. 360
Author(s):  
Catherine Vreugdenhil ◽  
Bishakhdatta Gayen
Keyword(s):  
Climate Change ◽  
Ocean Circulation ◽  
Mixed Layer ◽  
Water Mass ◽  
Current Knowledge ◽  
Open Ocean ◽  
Meridional Overturning Circulation ◽  
Ocean Dynamics ◽  
Global Circulation Models ◽  
Ocean Convection

Ocean convection is a key mechanism that regulates heat uptake, water-mass transformation, CO2 exchange, and nutrient transport with crucial implications for ocean dynamics and climate change. Both cooling to the atmosphere and salinification, from evaporation or sea-ice formation, cause surface waters to become dense and down-well as turbulent convective plumes. The upper mixed layer in the ocean is significantly deepened and sustained by convection. In the tropics and subtropics, night-time cooling is a main driver of mixed layer convection, while in the mid- and high-latitude regions, winter cooling is key to mixed layer convection. Additionally, at higher latitudes, and particularly in the sub-polar North Atlantic Ocean, the extensive surface heat loss during winter drives open-ocean convection that can reach thousands of meters in depth. On the Antarctic continental shelf, polynya convection regulates the formation of dense bottom slope currents. These strong convection events help to drive the immense water-mass transport of the globally-spanning meridional overturning circulation (MOC). However, convection is often highly localised in time and space, making it extremely difficult to accurately measure in field observations. Ocean models such as global circulation models (GCMs) are unable to resolve convection and turbulence and, instead, rely on simple convective parameterizations that result in a poor representation of convective processes and their impact on ocean circulation, air–sea exchange, and ocean biology. In the past few decades there has been markedly more observations, advancements in high-resolution numerical simulations, continued innovation in laboratory experiments and improvement of theory for ocean convection. The impacts of anthropogenic climate change on ocean convection are beginning to be observed, but key questions remain regarding future climate scenarios. Here, we review the current knowledge and future direction of ocean convection arising from sea–surface interactions, with a focus on mixed layer, open-ocean, and polynya convection.

scholarly journals Global Heat Balance and Heat Uptake in Potential Temperature Coordinates

2021 ◽  
Author(s):  
Antoine Hochet ◽  
Remi Tailleux ◽  
Till Kuhlbrodt ◽  
David Ferreira
Keyword(s):  
Global Warming ◽  
Water Mass ◽  
Potential Temperature ◽  
Effective Diffusion ◽  
Mitigation Strategies ◽  
Ocean Heat Uptake ◽  
Cold Temperatures ◽  
Advection Diffusion Equation ◽  
Advection Diffusion ◽  
Heat Uptake

Abstract The representation of ocean heat uptake in Simple Climate Models used for policy advice on climate change mitigation strategies is often based on variants of the one-dimensional Vertical Advection/Diffusion equation (VAD) for some averaged form of potential temperature. In such models, the effective advection and turbulent diffusion are usually tuned to emulate the behaviour of a given target climate model. However, because the statistical nature of such a \behavioural" calibration usually obscures the exact dependence of the effective diffusion and advection on the actual physical processes responsible for ocean heat uptake, it is difficult to understand its limitations and how to go about improving VAD. This paper proposes a physical calibration of the VAD that aims to provide explicit traceability of effective diffusion and advection to the processes responsible for ocean heat uptake. This construction relies on the coarse-graining of the full three-dimensional advection diffusion for potential temperature using potential temperature coordinates. The main advantage of this formulation is that the temporal evolution of the reference temperature profile is entirely due to the competition between effective diffusivity that is always positive definite, and the water mass transformation taking place at the surface, as in classical water mass analyses literature. These quantities are evaluated in numerical simulations of present day climate and global warming experiments. In this framework, the heat uptake in the global warming experiment is attributed to the increase of surface heat flux at low latitudes, its decrease at high latitudes and to the redistribution of heat toward cold temperatures made by diffusive flux.

Eddy-permitting simulations of the sub-polar North Atlantic: impact of the model bias on water mass properties and circulation

2010 ◽  
Vol 60 (5) ◽  
pp. 1177-1192 ◽  
Author(s):  
Jieshun Zhu ◽  
Entcho Demirov ◽  
Fred Dupont ◽  
Daniel Wright
Keyword(s):  
North Atlantic ◽  
Water Mass ◽  
Model Bias ◽  
Mass Properties
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