scholarly journals Characteristics of the deep ocean carbon system during the past 150,000 years:  CO2 distributions, deep water flow patterns, and abrupt climate change

1997 ◽  
Vol 94 (16) ◽  
pp. 8300-8307 ◽  
Author(s):  
E. A. Boyle
Keyword(s):  
Climate Change ◽  
Water Flow ◽  
Deep Water ◽  
Deep Ocean ◽  
Flow Patterns ◽  
Abrupt Climate Change ◽  
The Past ◽  
Ocean Carbon ◽  
Carbon System

scholarly journals Glacial – interglacial atmospheric CO<sub>2</sub> change: a simple "hypsometric effect" on deep-ocean carbon sequestration?

2006 ◽  
Vol 2 (5) ◽  
pp. 711-743 ◽  
Author(s):  
L. C. Skinner
Keyword(s):  
Carbon Sequestration ◽  
Carbon Storage ◽  
Ocean Circulation ◽  
Deep Water ◽  
Deep Sea ◽  
Storage Capacity ◽  
Deep Ocean ◽  
Contributing Factors ◽  
Carbon Reservoir ◽  
Ocean Carbon

Abstract. Given the magnitude and dynamism of the deep marine carbon reservoir, it is almost certain that past glacial – interglacial fluctuations in atmospheric CO2 have relied at least in part on changes in the carbon storage capacity of the deep sea. To date, physical ocean circulation mechanisms that have been proposed as viable explanations for glacial – interglacial CO2 change have focussed almost exclusively on dynamical or kinetic processes. Here, a simple mechanism is proposed for increasing the carbon storage capacity of the deep sea that operates via changes in the volume of southern-sourced deep-water filling the ocean basins, as dictated by the hypsometry of the ocean floor. It is proposed that a water-mass that occupies more than the bottom 3 km of the ocean will essentially determine the carbon content of the marine reservoir. Hence by filling this interval with southern-sourced deep-water (enriched in dissolved CO2 due to its particular mode of formation) the amount of carbon sequestered in the deep sea may be greatly increased. A simple box-model is used to test this hypothesis, and to investigate its implications. It is suggested that up to 70% of the observed glacial – interglacial CO2 change might be explained by the replacement of northern-sourced deep-water below 2.5 km water depth by its southern counterpart. Most importantly, it is found that an increase in the volume of southern-sourced deep-water allows glacial CO2 levels to be simulated easily with only modest changes in Southern Ocean biological export or overturning. If incorporated into the list of contributing factors to marine carbon sequestration, this mechanism may help to significantly reduce the "deficit" of explained glacial – interglacial CO2 change.

scholarly journals Glacial – interglacial atmospheric CO<sub>2</sub> change: a possible "standing volume" effect on deep-ocean carbon sequestration

2009 ◽  
Vol 5 (3) ◽  
pp. 1259-1296 ◽  
Author(s):  
L. C. Skinner
Keyword(s):  
Carbon Sequestration ◽  
Deep Water ◽  
Deep Sea ◽  
Deep Ocean ◽  
Volume Effect ◽  
Biological Pump ◽  
Mixing Rates ◽  
Water Filling ◽  
Ocean Carbon ◽  
Oceanic Carbon

Abstract. So far, the exploration of possible mechanisms for glacial atmospheric CO2 draw-down and marine carbon sequestration has focussed almost exclusively on dynamic or kinetic processes (i.e. variable mixing-, equilibration- or export rates). Here an attempt is made to underline instead the possible importance of changes in the standing volumes of intra-oceanic carbon reservoirs (i.e. different water-masses) in setting the total marine carbon inventory. By way of illustration, a simple mechanism is proposed for enhancing the carbon storage capacity of the deep sea, which operates via an increase in the volume of relatively carbon-enriched AABW-like deep-water filling the ocean basins. Given the hypsometry of the ocean floor and an active biological pump, the water-mass that fills more than the bottom 3 km of the ocean will essentially determine the carbon content of the marine reservoir. A set of simple box-model experiments confirm the expectation that a deep sea dominated by AABW-like deep-water holds more CO2, prior to any additional changes in ocean overturning rate, biological export or ocean-atmosphere exchange. The magnitude of this "standing volume effect" might be as large as the contributions that have been attributed to carbonate compensation, the thermodynamic solubility pump or the biological pump for example. If incorporated into the list of factors that have contributed to marine carbon sequestration during past glaciations, this standing volume mechanism may help to reduce the amount of glacial – interglacial CO2 change that remains to be explained by other mechanisms that are difficult to assess in the geological archive, such as reduced mass transport or mixing rates in particular. This in turn could help narrow the search for forcing conditions capable of pushing the global carbon cycle between glacial and interglacial modes.

scholarly journals The Evolution of Subantarctic Fronts, Deep Ocean Ventilation and Flow Vigour at the Agulhas Plateau: Surface-Deep Coupling Across Climate Transitions of the past 3 Ma

2020 ◽  
Author(s):  
Aidan Starr ◽  
Ian R. Hall ◽  
Stephen Barker ◽  
Jeroen van der Lubbe ◽  
Sidney R. Hemming ◽  
...  
Keyword(s):  
Ocean Circulation ◽  
Deep Water ◽  
Deep Ocean ◽  
Flow Speed ◽  
Bulk Sediment ◽  
Sediment Composition ◽  
The Past ◽  
Flow Speeds ◽  
Deep Ocean Circulation ◽  
Agulhas Plateau

&lt;p&gt;The geometry of large-scale deep ocean circulation is closely linked to processes occurring in the Southern Ocean (SO). The SO is the &amp;#8216;window&amp;#8217; through which much of the world&amp;#8217;s ocean interior interacts with the atmosphere, and understanding the complex relationships coupling SO dynamics to deep circulation can provide valuable insights into biogeochemical and physical processes important to global climate. Of particular interest is how these processes interacted with, and behaved under different climate states, such as the glacial-interglacial cycles of the Pleistocene (0-2.8 Ma), and the intensification of Northern Hemisphere glaciation during the transition from the warm Mid-Pliocene (3.3-3.1 Ma) to the early Pleistocene. Here, we utilise new composite sediment core records (41&lt;sup&gt;o&lt;/sup&gt;S, 25&lt;sup&gt;o&lt;/sup&gt;E, 2700-2900 m water depth) to reconstruct deep chemical and physical ventilation at the Agulhas Plateau, as well as the competing presence of warm Subtropical waters vs cold Subantarctic waters in the surface, over the past ~3 Ma. We present records of the &amp;#8216;sortable silt&amp;#8217; flow speed proxy, the stable isotope (&amp;#948;&lt;sup&gt;18&lt;/sup&gt;O, &amp;#948;&lt;sup&gt;13&lt;/sup&gt;C) composition of benthic foraminifera, bulk sediment element concentrations, and the accumulation of ice-rafted debris (IRD). The sortable silt proxy demonstrates that deep physical ventilation is largely decoupled from deep chemical ventilation as indicated by benthic &amp;#948;&lt;sup&gt;13&lt;/sup&gt;C, with higher flow speeds coincident with more depleted &amp;#948;&lt;sup&gt;13&lt;/sup&gt;C. Furthermore, deep ventilation is related to changes in the terrigenous sediment composition: deep flow speeds and &amp;#948;&lt;sup&gt;13&lt;/sup&gt;C vary concurrently with bulk sediment geochemistry (K/Al, Ti). At the Agulhas Plateau, we interpret deep chemical ventilation and near-bottom flow speeds to reflect changes in the advection of northern-sourced deep waters (e.g. North Atlantic Deep Water and its glacial equivalent) and meridional variability in the location of the deep-reaching Antarctic Circumpolar Current (ACC) and its associated fronts. The presence of IRD at the Agulhas Plateau is controlled primarily by the equatorward survivability far-travelling Antarctic icebergs, and therefore represents the relative presence of cold, iceberg-bearing Subantarctic Zone (SAZ) surface waters. Generally, at times of high near-bottom flow speed and more &amp;#8216;southern&amp;#8217; terrigenous sediment composition, IRD is higher, implying a meridional expansion of the SAZ. Together, these proxy records provide a continuous and long-term insight into the evolution of coupled surface-deep conditions at the Agulhas Plateau. We postulate that these conditions may reflect the wider geometry of ocean circulation in the SO, documenting the interactions between the ACC and circum-Antarctic fronts with the upwelling, conversion, and export of deep water masses. Our records represent the first multi-proxy reconstruction of this system across climate transitions of the past ~3 Ma, allowing us to explore its evolution across a range of timescales, from million-year to orbital-scale. Furthermore, by measuring multiple proxies on the same samples, we are able to determine the relative phasing between different processes independent of chronostratigraphic uncertainties, for example the timing of SAZ changes vs perturbations in deep ocean circulation at the site.&amp;#160; &amp;#160;&lt;/p&gt;

scholarly journals Glacial-interglacial atmospheric CO<sub>2</sub> change: a possible "standing volume" effect on deep-ocean carbon sequestration

2009 ◽  
Vol 5 (3) ◽  
pp. 537-550 ◽  
Author(s):  
L. C. Skinner
Keyword(s):  
Carbon Sequestration ◽  
Deep Water ◽  
Deep Ocean ◽  
Volume Effect ◽  
Lower Circumpolar Deep Water ◽  
Mixing Rates ◽  
Ocean Carbon ◽  
Oceanic Carbon ◽  
Global Carbon ◽  
Carbon Inventory

Abstract. So far, the exploration of possible mechanisms for glacial atmospheric CO2 drawdown and marine carbon sequestration has tended to focus on dynamic or kinetic processes (i.e. variable mixing-, equilibration- or export rates). Here an attempt is made to underline instead the possible importance of changes in the standing volumes of intra-oceanic carbon reservoirs (i.e. different water-masses) in influencing the total marine carbon inventory. By way of illustration, a simple mechanism is proposed for enhancing the marine carbon inventory via an increase in the volume of relatively cold and carbon-enriched deep water, analogous to modern Lower Circumpolar Deep Water (LCDW), filling the ocean basins. A set of simple box-model experiments confirm the expectation that a deep sea dominated by an expanded LCDW-like watermass holds more CO2, without any pre-imposed changes in ocean overturning rate, biological export or ocean-atmosphere exchange. The magnitude of this "standing volume effect" (which operates by boosting the solubility- and biological pumps) might be as large as the contributions that have previously been attributed to carbonate compensation, terrestrial biosphere reduction or ocean fertilisation for example. By providing a means of not only enhancing but also driving changes in the efficiency of the biological- and solubility pumps, this standing volume mechanism may help to reduce the amount of glacial-interglacial CO2 change that remains to be explained by other mechanisms that are difficult to assess in the geological archive, such as reduced mass transport or mixing rates in particular. This in turn could help narrow the search for forcing conditions capable of pushing the global carbon cycle between glacial and interglacial modes.

scholarly journals Transition process of abrupt climate change based on global sea surface temperature over the past century

2016 ◽  
Vol 23 (3) ◽  
pp. 115-126 ◽  
Author(s):  
Pengcheng Yan ◽  
Wei Hou ◽  
Guolin Feng
Keyword(s):  
Climate Change ◽  
Climate Changes ◽  
Transition Process ◽  
Sea Surface ◽  
Abrupt Climate Change ◽  
Past Century ◽  
The Past ◽  
The Relationship ◽  
Global Sea Surface Temperature ◽  
State Moment

Abstract. A new detection method has been proposed to study the transition process of abrupt climate change. With this method, the climate system transiting from one stable state to another can be verified clearly. By applying this method to the global sea surface temperature over the past century, several climate changes and their processes are detected, including the start state (moment), persist time, and end state (moment). According to the spatial distribution, the locations of climate changes mainly have occurred in the Indian Ocean and western Pacific before the middle twentieth century, in the 1970s in the equatorial middle-eastern Pacific, and in the middle and southern Pacific since the end of the twentieth century. In addition, the quantitative relationship between the transition process parameters is verified in theory and practice: (1) the relationship between the rate and stability parameters is linear, and (2) the relationship between the rate and change amplitude parameters is quadratic.

Can Radiocarbon Records lead to Quantitative Estimates of Deep-Ocean Ventilation Rates with Error Estimates in the Geologic Past?

2020 ◽  
Author(s):  
Olivier Marchal ◽  
Ning Zhao ◽  
Faith Duffy
Keyword(s):  
Least Squares ◽  
Error Estimates ◽  
Deep Water ◽  
Benthic Foraminifera ◽  
Deep Ocean ◽  
The Past ◽  
Ocean Ventilation ◽  
Quantitative Estimates ◽  
History Of ◽  
Ventilation Rates

&lt;p&gt;Over the past two decades, an impressive amount of radiocarbon age measurements on samples of fossil benthic foraminifera and deep-sea corals have been published in the literature. These measurements are commonly used to draw inferences about changes in the ventilation of deep oceanic basins during the last deglacial period. Lacking in most previous studies, however, are quantitative estimates of deep-ocean paleo-ventilation rates and quantitative estimates of their errors, leading to potential over-interpretation and sterile debate. Moreover, most previous studies were concerned with the interpretation of individual records with low or no regard for other records available for the same time interval.&lt;/p&gt;&lt;p&gt;Here we present an effort to go beyond the qualitative interpretation of single radiocarbon records by analyzing an updated compilation of &lt;sup&gt;14&lt;/sup&gt;C age data using recursive least-squares (RLS) methods (a Kalman filter and a related smoother). In stark contrast with other methods of data analysis, RLS methods can provide an estimate of the history of the state of the physical system of interest and an estimate of the error in this history, which are consistent (in the least-squares sense) with times series of data and with a dynamical model, given estimates of the statistics of the errors in the data and in the model. Our current compilation includes 1,698 deep water &lt;sup&gt;14&lt;/sup&gt;C age data for the past 40&amp;#160;kyr based on fossil samples of benthic foraminifera, deep&amp;#8208;sea corals, deep&amp;#8208;dwelling planktonic foraminifera, bivalves, and spiral shells. The geographic distribution of the samples is very irregular, with most of them originating from near the margins and with large regions devoid of any data. The depths of the samples vary from about 250&amp;#160;m to about 5,000&amp;#160;m. In our study, the potential of RLS methods to estimate the history of deep-ocean ventilation rates and their errors from deep water &lt;sup&gt;14&lt;/sup&gt;C age data is explored for a number of abyssal layers in the Atlantic Ocean during the deglacial interval from 20 to 10 kyr BP. The approach used to apply the powerful but computationally expensive RLS methods to the analysis of geologic time series is described, the least-squares estimates of ventilation rate history in different layers are reported, and their significance in the light of their error estimates is discussed.&lt;/p&gt;

Zonal asymmetry of Southern Ocean air-sea carbon fluxes

2021 ◽  
Author(s):  
Channing Prend ◽  
Alison Gray ◽  
Lynne Talley ◽  
Sarah Gille ◽  
Alexander Haumann ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Mixed Layer ◽  
Deep Water ◽  
Carbon Sink ◽  
Deep Ocean ◽  
Carbon Fluxes ◽  
Regional Variability ◽  
Zonal Asymmetry ◽  
Ocean Carbon ◽  
Using Data

&lt;p&gt;The Southern Ocean modulates the climate system by exchanging heat and carbon dioxide (CO&lt;sub&gt;2&lt;/sub&gt;) between the atmosphere and deep ocean. While this region plays an outsized role in the global oceanic anthropogenic carbon uptake, CO&lt;sub&gt;2&lt;/sub&gt; is released into the atmosphere across large swaths of the Antarctic Circumpolar Current (ACC). Southern Ocean outgassing has long been attributed to remineralized carbon from upwelled deep water, but the precise mechanisms by which this water reaches the surface are not well known. Using data from a novel array of autonomous biogeochemical profiling floats, we estimate Southern Ocean air-sea CO&lt;sub&gt;2&lt;/sub&gt; fluxes at unprecedented spatial resolution and determine the pathways that transfer carbon from the ocean interior into the mixed layer where air-sea exchange occurs. Float-based flux estimates suggest that carbon outgassing occurs predominantly in the Indo-Pacific sector of the ACC due to variations in the mean surface ocean partial pressure of CO&lt;sub&gt;2&lt;/sub&gt; (&lt;em&gt;p&lt;/em&gt;CO&lt;sub&gt;2&lt;/sub&gt;). Within the Polar Frontal Zone and Antarctic Southern Zone of the ACC, the annual mean &lt;em&gt;p&lt;/em&gt;CO&lt;sub&gt;2&lt;/sub&gt; difference between the Indo-Pacific and Atlantic is 40.1 &amp;#177; 12.9 &amp;#956;atm and 17.9 &amp;#177; 12.4 &amp;#956;atm, respectively. We show that this zonal asymmetry in surface &lt;em&gt;p&lt;/em&gt;CO&lt;sub&gt;2&lt;/sub&gt; and consequently air-sea carbon fluxes stems from regional variability in the mixed-layer entrainment of carbon-rich deep water. These results suggest that long-term trends of the Southern Ocean carbon sink inferred from sparse shipboard data may depend on the fraction of measurements from each basin in a given year. Furthermore, sampling these different air-sea flux regimes is necessary to monitor future changes in oceanic carbon release and uptake.&lt;/p&gt;

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