scholarly journals High-latitude ocean ventilation and its role in Earth's climate transitions

2017 ◽  
Vol 375 (2102) ◽  
pp. 20160324 ◽  
Author(s):  
Alberto C. Naveira Garabato ◽  
Graeme A.  MacGilchrist ◽  
Peter J. Brown ◽  
D. Gwyn Evans ◽  
Andrew J. S. Meijers ◽  
...  
Keyword(s):  
Ocean Circulation ◽  
High Latitude ◽  
Climate System ◽  
High Latitudes ◽  
Overturning Circulation ◽  
Ocean Ventilation ◽  
Earth’S Climate ◽  
Warming World ◽  
Climate Transitions

The processes regulating ocean ventilation at high latitudes are re-examined based on a range of observations spanning all scales of ocean circulation, from the centimetre scales of turbulence to the basin scales of gyres. It is argued that high-latitude ocean ventilation is controlled by mechanisms that differ in fundamental ways from those that set the overturning circulation. This is contrary to the assumption of broad equivalence between the two that is commonly adopted in interpreting the role of the high-latitude oceans in Earth's climate transitions. Illustrations of how recognizing this distinction may change our view of the ocean's role in the climate system are offered. This article is part of the themed issue ‘Ocean ventilation and deoxygenation in a warming world’.

scholarly journals Ocean ventilation and deoxygenation in a warming world: introduction and overview

2017 ◽  
Vol 375 (2102) ◽  
pp. 20170240 ◽  
Author(s):  
John G. Shepherd ◽  
Peter G. Brewer ◽  
Andreas Oschlies ◽  
Andrew J. Watson
Keyword(s):  
Climate Change ◽  
Ocean Circulation ◽  
Economic Consequences ◽  
Oxygen Solubility ◽  
Ocean Ventilation ◽  
Wide Range ◽  
Indirect Impacts ◽  
Warming World ◽  
Ventilation Rates ◽  
Oral Presentations

Changes of ocean ventilation rates and deoxygenation are two of the less obvious but important indirect impacts expected as a result of climate change on the oceans. They are expected to occur because of (i) the effects of increased stratification on ocean circulation and hence its ventilation, due to reduced upwelling, deep-water formation and turbulent mixing, (ii) reduced oxygenation through decreased oxygen solubility at higher surface temperature, and (iii) the effects of warming on biological production, respiration and remineralization. The potential socio-economic consequences of reduced oxygen levels on fisheries and ecosystems may be far-reaching and significant. At a Royal Society Discussion Meeting convened to discuss these matters, 12 oral presentations and 23 posters were presented, covering a wide range of the physical, chemical and biological aspects of the issue. Overall, it appears that there are still considerable discrepancies between the observations and model simulations of the relevant processes. Our current understanding of both the causes and consequences of reduced oxygen in the ocean, and our ability to represent them in models are therefore inadequate, and the reasons for this remain unclear. It is too early to say whether or not the socio-economic consequences are likely to be serious. However, the consequences are ecologically, biogeochemically and climatically potentially very significant, and further research on these indirect impacts of climate change via reduced ventilation and oxygenation of the oceans should be accorded a high priority. This article is part of the themed issue ‘Ocean ventilation and deoxygenation in a warming world’.

scholarly journals The role of ice in N<sub>2</sub>O<sub>5</sub> heterogeneous hydrolysis at high latitudes

2008 ◽  
Vol 8 (4) ◽  
pp. 12595-12624 ◽  
Author(s):  
R. L. Apodaca ◽  
D. M. Huff ◽  
W. R. Simpson
Keyword(s):  
Steady State ◽  
Nitric Acid ◽  
Surface Area ◽  
High Latitude ◽  
Acid Production ◽  
High Latitudes ◽  
Air Masses ◽  
Mixing Ratios ◽  
Reactive Surfaces

Abstract. We report evidence for ice catalyzing N2O5 heterogeneous hydrolysis from a study conducted near Fairbanks, AK in November 2007. Mixing ratios of N2O5, NO, NO2, and ozone are reported and are used to determine steady state N2O5 lifetimes. When air masses are sub-saturated with respect to ice, the data show longer lifetimes (≈20 min) and elevated N2O5 levels, while ice-saturated air masses show shorter lifetimes (≈6 min) and suppressed N2O5 levels. We also report estimates of aerosol surface area densities that are on the order of 50 μm2/cm3, a surface area density that is insufficient to explain the rapid losses of N2O5 observed in this study, reinforcing the importance of other reactive surfaces such as ice. Ice-saturated pollution plumes are ubiquitous in high latitudes; therefore, catalysis on these surfaces is largely responsible for nocturnal processing of N2O5 leading to nitric acid production and loss of NOx in high latitude plumes.

scholarly journals An Interhemispheric Four-Box Model of the Meridional Overturning Circulation

2011 ◽  
Vol 41 (3) ◽  
pp. 516-530 ◽  
Author(s):  
Peter H. Stone ◽  
Yuriy P. Krasovskiy
Keyword(s):  
High Latitude ◽  
General Circulation ◽  
Circulation Model ◽  
Meridional Overturning Circulation ◽  
High Latitudes ◽  
Stable States ◽  
Low Latitude ◽  
Overturning Circulation ◽  
High Latitude Region ◽  
Meridional Overturning

Abstract The authors introduce a four-box interhemispheric model of the meridional overturning circulation. A single box represents high latitudes in each hemisphere, and in contrast to earlier interhemispheric box models, low latitudes are represented by two boxes—a surface box and a deep box—separated by a thermocline in which a balance is assumed between vertical advection and vertical diffusion. The behavior of the system is analyzed with two different closure assumptions for how the low-latitude upwelling depends on the density contrast between the surface and deep low-latitude boxes. The first is based on the conventional assumption that the diffusivity is a constant, and the second on the assumption that the energy input to the mixing is constant. There are three different stable equilibrium states that are closely analogous to the three found by Bryan in a single-basin interhemispheric ocean general circulation model. One is quasi-symmetric with downwelling in high latitudes of both hemispheres, and two are asymmetric solutions, with downwelling confined to high latitudes in one or the other of the two hemispheres. The quasi-symmetric solution becomes linearly unstable for strong global hydrological forcing, while the two asymmetric solutions do not. The qualitative nature of the solutions is generally similar for both the closure assumptions, in contrast to the solutions in hemispheric models. In particular, all the stable states can be destabilized by finite amplitude perturbations in the salinity or the hydrological forcing, and transitions are possible between any two states. For example, if the system is in an asymmetric state, and the moisture flux into the high-latitude region of downwelling is slowly increased, for both closure assumptions the high-latitude downwelling decreases until a critical forcing is reached where the system switches to the asymmetric state with downwelling in the opposite hemisphere. By contrast, in hemispheric models with the energy constraint, the downwelling increases and there is no loss of stability.

scholarly journals The Earth’s climate system recurrent & multi-scale lagged responses: empirical law, evidence, consequent solar explanation of recent CO<sub>2</sub> increases & preliminary analysis

2016 ◽  
Author(s):  
Jorge Sánchez-Sesma
Keyword(s):  
Solar Activity ◽  
Ocean Circulation ◽  
Volcanic Activity ◽  
Tropical Climate ◽  
Meridional Overturning Circulation ◽  
Climate System ◽  
Global Ocean ◽  
Climate Modelling ◽  
Climate Signal ◽  
Earth’S Climate

Abstract. This paper analyzes the lagged responses of the Earth’s climate system, as part of cosmic-solar-terrestrial processes. Firstly, we analyze and model the lagged responses of the Earth’s climate system, previously detected for geological and orbital scale processes, with simple non-linear functions, and we estimate a correspondent lag of ~1600-yr for the recently detected ~9500-yr scale solar recurrent patterns. Secondly, a recurrent and lagged linear influence of solar variation on volcanic activity and carbon dioxide (CO2) has been assessed for the last millennia, and extrapolated for future centuries and millennia. As a consequence we found that, on one side, the recent CO2 increase can be considered as a lagged response to solar activity, and, on the other side, the continental tropical climate signal during late Holocene can be considered as a sum of three lagged responses to solar activity, through direct, and indirect (volcanic and CO2), influences with different lags of around 40, 800 and 1600 years. Thirdly, we find more examples of this ~1600-yr lag, associated with oceanic processes throughout the Holocene, manifested in the mineral content of SE Pacific waters, and in a carbon cycle index, CO3, in the Southern Atlantic. Fourthly, we propose the global ocean circulation processes, that include the well known meridional overturning circulation, and the thermohaline circulation, as a global mechanism capable of explaining the lagged forcing (volcanic activity &amp; CO2) and continental tropical climate responses to solar activity variations. Finally, some conclusions are provided for the lagged responses of the Earth's climate system with their influences and consequences on present and future climate, and implications for climate modelling are preliminarily analyzed.

scholarly journals Locations and Mechanisms of Ocean Ventilation in the High-Latitude North Atlantic in an Eddy-Permitting Ocean Model

2020 ◽  
Vol 33 (23) ◽  
pp. 10113-10131
Author(s):  
Graeme A. MacGilchrist ◽  
Helen L. Johnson ◽  
David P. Marshall ◽  
Camille Lique ◽  
Matthew Thomas ◽  
...  
Keyword(s):  
Ocean Circulation ◽  
North Atlantic ◽  
High Latitude ◽  
Circulation Model ◽  
Deep Ocean ◽  
Ocean Model ◽  
Surface Mixed Layer ◽  
Boundary Current ◽  
Important Distinction ◽  
Ocean Ventilation

AbstractA substantial fraction of the deep ocean is ventilated in the high-latitude North Atlantic. Consequently, the region plays a crucial role in transient climate change through the uptake of carbon dioxide and heat. However, owing to the Lagrangian nature of the process, many aspects of deep Atlantic Ocean ventilation and its representation in climate simulations remain obscure. We investigate the nature of ventilation in the high-latitude North Atlantic in an eddy-permitting numerical ocean circulation model using a comprehensive set of Lagrangian trajectory experiments. Backward-in-time trajectories from a model-defined North Atlantic Deep Water (NADW) reveal the locations of subduction from the surface mixed layer at high spatial resolution. The major fraction of NADW ventilation results from subduction in the Labrador Sea, predominantly within the boundary current (~60% of ventilated NADW volume) and a smaller fraction arising from open ocean deep convection (~25%). Subsurface transformations—due in part to the model’s parameterization of bottom-intensified mixing—facilitate NADW ventilation, such that water subducted in the boundary current ventilates all of NADW, not just the lighter density classes. There is a notable absence of ventilation arising from subduction in the Greenland–Iceland–Norwegian Seas, due to the re-entrainment of those waters as they move southward. Taken together, our results emphasize an important distinction between ventilation and dense water formation in terms of the location where each takes place, and their concurrent sensitivities. These features of NADW ventilation are explored to understand how the representation of high-latitude processes impacts properties of the deep ocean in a state-of-the-science numerical simulation.

scholarly journals 2017 program of studies: ice-ocean interactions

2018 ◽  
Author(s):  
Claudia Cenedese ◽  
Mary-Louise Timmermans
Keyword(s):  
Climate Change ◽  
Fluid Dynamics ◽  
Ocean Circulation ◽  
High Latitude ◽  
Ocean Dynamics ◽  
Geophysical Fluid Dynamics ◽  
Study Program ◽  
Ice Sheet Dynamics ◽  
Summer Study

The 2017 Geophysical Fluid Dynamics Summer Study Program theme was Ice-Ocean Interactions. Three principal lecturers, Andrew Fowler (Oxford), Adrian Jenkins (British Antarctic Survey) and Fiamma Straneo (WHOI/Scripps Institution of Oceanography) were our expert guides for the first two weeks. Their captivating lectures covered topics ranging from the theoretical underpinnings of ice-sheet dynamics, to models and observations of ice-ocean interactions and high-latitude ocean circulation, to the role of the cryosphere in climate change. These icy topics did not end after the first two weeks. Several of the Fellows' projects related to ice-ocean dynamics and thermodynamics, and many visitors gave talks on these themes.

scholarly journals The role of ice in N<sub>2</sub>O<sub>5</sub> heterogeneous hydrolysis at high latitudes

2008 ◽  
Vol 8 (24) ◽  
pp. 7451-7463 ◽  
Author(s):  
R. L. Apodaca ◽  
D. M. Huff ◽  
W. R. Simpson
Keyword(s):  
Steady State ◽  
Nitric Acid ◽  
Surface Area ◽  
High Latitude ◽  
High Latitudes ◽  
Air Masses ◽  
Mixing Ratios ◽  
Ice Surfaces ◽  
Reactive Surfaces

Abstract. We report evidence for ice catalyzing N2O5 heterogeneous hydrolysis from a study conducted near Fairbanks, Alaska in November 2007. Mixing ratios of N2O5, NO, NO2, and ozone are reported and are used to determine steady state N2O5 lifetimes. When air masses are sub-saturated with respect to ice, the data show longer lifetimes (≈20 min) and elevated N2O5 levels, while ice-saturated air masses show shorter lifetimes (≈6 min) and suppressed N2O5 levels. We also report estimates of aerosol surface area densities that are on the order of 50 μm2/cm3, a surface area density that is insufficient to explain the rapid losses of N2O5 observed in this study, reinforcing the importance of other reactive surfaces such as ice. Consideration of two possible responsible types of ice surfaces, the snowpack and suspended ice particles, indicates that both are reasonable as possible sinks for N2O5. Because ice-saturated conditions are ubiquitous in high latitudes, ice surfaces are likely to be a key loss of N2O5, leading to nitric acid production and loss of NOx in high latitude plumes.

The role of changing Southern Ocean circulation for the uptake and storage of CFC-12, anthropogenic CO2 and oxygen

2020 ◽  
Author(s):  
Lavinia Patara ◽  
Jan Klaus Rieck ◽  
Toste Tanhua ◽  
Iris Kriest ◽  
Claus Boening
Keyword(s):  
Southern Ocean ◽  
Ocean Circulation ◽  
Carbon Sink ◽  
Biogeochemical Model ◽  
Low Oxygen ◽  
Ocean Ventilation ◽  
First Results ◽  
Ocean Carbon ◽  
And Storage

&lt;p&gt;Recent studies highlighted an increase in the Southern Ocean ventilation since several decades and, at the same time, pronounced decadal fluctuations in its carbon sink. The role of changing ventilation for the anthropogenic CO&lt;sub&gt;2&lt;/sub&gt; uptake (and thus for the overall Southern Ocean carbon sink) and for oxygen concentrations of mode and intermediate waters (with possible impacts on low-oxygen regions downstream) are still poorly understood. The aim of this study is to assess the role of changing Southern Ocean ventilation for the uptake and storage of atmospheric gases such as CFC-12, CO&lt;sub&gt;2&lt;/sub&gt; and oxygen. A related question is whether CFC-12 can be used as a proxy of anthropogenic CO&lt;sub&gt;2&lt;/sub&gt; in the Southern Ocean, since CO&lt;sub&gt;2&lt;/sub&gt; equilibrates significantly more slowly in seawater than CFC-12 and, while the solubility of CFC-12 increases with decreasing temperature and salinity, the solubility of anthropogenic CO&lt;sub&gt;2&lt;/sub&gt; decreases. We developed a suite of global configurations based on the NEMO-LIM2 ocean sea ice model including the passive tracer CFC-12 and the biogeochemical model MOPS. The suite includes ORCA05 (1/2&amp;#176; resolution), ORCA025 (1/4&amp;#176; resolution) and ORION10 (featuring a 1/10&amp;#176; nest between 68&amp;#176;S and 30&amp;#176;S). Hindcast and sensitivity experiments performed with ORCA025 under the JRA-55-do atmospheric forcing are used to unravel the role of changing wind and buoyancy forcing on the gas uptake and storage. First results highlight that anthropogenic CO&lt;sub&gt;2&lt;/sub&gt; is taken up in lighter density classes than CFC-12, meaning that increased ventilation of lighter mode waters would be particularly effective in taking up anthropogenic CO&lt;sub&gt;2&lt;/sub&gt;. This effect is more pronounced in the higher-resolution model ORION10, indicating that mesoscale eddies inject anthropogenic CO&lt;sub&gt;2&lt;/sub&gt; in lighter waters than lower-resolution models.&lt;/p&gt;

scholarly journals Crafting a public for geoengineering

2015 ◽  
Vol 26 (4) ◽  
pp. 402-417 ◽  
Author(s):  
Rob Bellamy ◽  
Javier Lezaun
Keyword(s):  
Global Warming ◽  
Public Engagement ◽  
Policy Option ◽  
Public Debate ◽  
Climate System ◽  
Short Period ◽  
Public Engagement With Science ◽  
Earth’S Climate

In a short period of time, climate ‘geoengineering’ has been added to the list of technoscientific issues subject to deliberative public engagement. Here, we analyse this rapid trajectory of publicization and explore the particular manner in which the possibility of intentionally altering the Earth’s climate system to curb global warming has been incorporated into the field of ‘public engagement with science’. We describe the initial framing of geoengineering as a singular object of debate and subsequent attempts to ‘unframe’ the issue by placing it within broader discursive fields. The tension implicit in these processes of structured debate – how to turn geoengineering into a workable object of deliberation without implying a commitment to its reality as a policy option – raises significant questions about the role of ‘public engagement with science’ scholars and methods in facilitating public debate on speculative technological futures.

Essentials of the Earth's Climate System

2014 ◽  
Author(s):  
Roger G. Barry ◽  
Eileen A. Hall-McKim
Keyword(s):  
Climate System ◽  
Earth’S Climate
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