The three l=1 Stokes coefficients corresponding to the geocenter motion are not included in the GRCAE data. Rev Geophys 24(3):469491. Antarctic Circumpolar Current flows more rapidly in warm phases For the ACC, Zlotnicki et al. 4a. Now one sees an EOF pattern that is essentially the sum of the EOF patterns of the two constituents, that is, the sum of Fig. doi:10.1029/2007JB005338, Tapley BD, Bettadpur S, Watkins M, Reigber C (2004) The gravity recovery and climate experiment: mission overview and early results. With the intensity of the fire aboard the car carrier Fremantle Highway continuing to dissipate, Dutch authorities announced late today that they are preparing to reposition the ship in the first of a series of steps that they anticipate will ultimately bring the wreck to a still to be determined port. As stated, we are interested in the broadband, intraseasonalinterannual variations minus the strong seasonality. 1); the reverse is true when the SAM Index is negative. b andc are the same as a but for two sub-timespans, January 2003December 2009 and January 2009July 2015, respectively. Bning et al. (2003) reported a slight warming over three decades at depths of 200900m in a region around 70E, 62S, suggesting that the Southern ACC Front had shifted southward. (2010; see also Bning et al. The two TVG constituent datasets are involved: The GAD dataset is one of the Atmosphere and Ocean De-aliasing Level-1B products utilized in the GRACE data pre-processing to avoid aliasing errors from atmospheric and oceanic signals higher in frequency than monthly. J Geophys Res Oceans 120(6):42454259. doi:10.1029/2010RG000348, Mo KC (2000) Relationships between low-frequency variability in the Southern Hemisphere and sea surface temperature anomalies. Specifically, it is the part of the non-tidal OBP as modeled by state-of-the-art atmosphereocean circulation models, including both barotropic and baroclinic effects. It is vital for Earths health because it keeps Antarctica cool and frozen. Since its launch in 2002, the twin-satellite mission of the Gravity Recovery and Climate Experiment (GRACE) (Tapley et al. To remove the non-target signals, we model the OBP time series processed above at any given grid point as: The polynomial accounts for a quadratic trend (including the mean), and the sinusoidal terms [where =2/(365.26days)] represent the annual and semi-annual seasonal signals. The ACC is an eastward geostrophic flow manifesting as a zonal circulation (clockwise when viewed from above Antarctica) typically in the form of series of fronts and turbulent jets around the Antarctica continent (e.g., Rintoul et al. Terms and Conditions, It displays a quasi-annular band surrounding and abutting the Antarctica continent, which undergoes a unison variation. w Specifically, the geostrophic equation governing the variation of the horizontal zonal component u (positive for eastward) and meridional component v (positive for northward) of the flow velocity accompanying the OBP variation P is: where denotes temporal change, In: GRACE technical note #07. This warmer part of the Southern Ocean has warmed even further due to climate change, leading to an increase in temperature differences between the regions north and south of the Circumpolar Current. J Geophys Res 113:B08410. The root of this discrepancy is presently unclear. Both are known to split into two or three branches in some parts of the Southern Ocean, and merge together in other parts. The Antarctic Circumpolar Current: A Conduit or Blender of Antarctic 2013; Abram et al. Parallel studies have been conducted for major ocean currents, for example the correlation found with the GRACE bottom pressure data and the Kuroshio Extension System Study array (Park et al. doi:10.5194/os-8-859-2012, Chao BF (2005) On inversion for mass distribution from global (time-variable) gravity field. Photo credit: Nathan Bindoff. 2012; Feng et al. White, black, and red arrows are respectively the Antarctic Circumpolar Current, the Antarctic Slope Current and Australian-Antarctic Basin gyre, and the East Australian Current. Figure2b, on the other hand, shows the leading EOF mode of the residual OBP P(t) from the GRACE GSM data. It is known that the ACC transport depends on the eastward wind stress over the Southern Ocean (Thompson and Wallace 2000). The question now is how this increased transfer of heat across the ACC will impact the stability of the Antarctic ice sheet, and consequently the rate of global sea-level rise. All rights reserved. The Maritime Executive, Published Meredith and Hogg (2006) found that the SAM leads the EKE of the ACC by 1.52years and proposed that the enhanced winds associated with an increasing SAM act to tilt isopycnals, which in turn increases the baroclinic instability. Ocean density increases as water gets colder and as it gets more salty. This relatively long-term change over the course of the past few decades is attributed to an increasing atmospheric concentration of ozone-depleting and greenhouse gases. Dr. Proctor is a geology, sustainability, and planetary science professor at South Mountain Community College, Phoenix, Arizona. In contrast, the mixing length does not depend on the mean flow in the subpolar zone, likely reflecting the relatively quiescent flow regime. This speedup of the ACC, especially its jet centered on the Subantarctic Front, facilitates property exchange, such as of heat or carbon, between ocean basins and creates the opportunity for these properties to increase in subsurface subtropical regions, Shi said. While not much change is seen along AA between the two 7-year half-timespans, the variation u along BB and CC in the later half-timespan differs significantly relative to the first half, thereof the peak u fluctuation between 60-65S increases from about 2 to 4mm/s. Part of 2007). Introduction. What Do IMO's New Climate Targets Mean for Shipping? A large body of recent oceanographic research has shown that the Antarctic Circumpolar Current (ACC), an ocean current that flows from west to east around Antarctica, plays a crucial role in global ocean circulation. - The New York Times Rising From the Antarctic, a Climate Alarm Wilder winds are altering currents. 2c, the corresponding time history stays the same as in Fig. Provided by the Springer Nature SharedIt content-sharing initiative. The coefficients are then estimated via linear least-squares regression, and the resultant analytical terms subtracted to yield the non-seasonal residual P(t). Once it surfaces, some of the water flows northward again and sinks north of the Subarctic Front. Waters south of the Polar Front are becoming fresher due to increased rainfall there, and waters to the north of the Polar Front are becoming saltier due to increased evaporation. To circumvent the numerical awkwardness of the shrinking spacing toward the poles in the conventional latitude/longitude gridding that calls for artificial area weighting of data (such as by the factor cos or alternatively its square root in computing the EOF), we resample the GRACE data into a uniform reduced Gaussian grid (N80) at nominal spacing of 125km with altogether 5196 grid points to be input to the EOF process. Warm circumpolar water passes through the Drake Passage and flows eastward in the Antarctic Circumpolar Current (red arrow). The high correlation of the associated time series with the SAM (being of course the same as Fig. lm Thanks to new measurements, a team of researchers from the University of California San Diego and other institutes has now been able to show that the circumpolar current has accelerated and narrowed since 1993. Map of the ocean surface temperature as measured by satellites and analysed by the European Copernicus Marine Services. It is also changing as the world's climate warms. For the cross-correlation function, positive lags mean that the SAM Index leads the EOF mode time series. We mention in passing that the combination of u and v suggests the presence of variations in the Ross Gyre also in pace with the SAM, whereas any more detailed study of it would entail, for instance, dedicated the regional EOF analysis which is beyond the scope here. Swenson et al. The TVG data were available from the GRACE Project and the Center for Space Research, University of Texas. The Maritime Executive. There is a growing concern that companies operating within the EU already face significant constraints on recycling capacity with will only get worse as the industry transitions away from older fossil fuel vessels to address emerging emissions standards. A negative SAM Index (on the left panel) signifies the opposite. When combined (as explained above), the non-seasonal P(t) of the GAD+GSM data yields the leading EOF mode shown in Fig. J Geodyn 72:7280. J Phys Ocean 37:230244. As a result of this expedition, the JR scientists will be able to document the paleoenvironmental history of the ACC so that we can better understand the impact of our current changing climate. November 29, 2021 Source: University of California - San Diego Summary: The Antarctic Circumpolar Current (ACC), the only ocean current that circumnavigates the planet, is speeding up. On the size of the Antarctic Circumpolar Current - ScienceDirect 3 and shows the peak correlation coefficient of 0.77 where the single prominent peak is at zero time shift. The ACC is a massive flow of water that acts as a barrier separating the Southern Ocean from more northern oceans. doi:10.1029/2007RG000231, Meredith MP, Hogg AMcC (2006) Circumpolar response of Southern Ocean eddy activity to a change in the Southern Annular Mode. 2023 BioMed Central Ltd unless otherwise stated. Also shows that we are currently at the dangerously low, not dangerously high, end of a wide and safe range of CO2 concentrations. Currently the Antarctic Peninsula is undergoing extraordinary climate change. It is produced using 23 years of satellite altimetry (ocean height) observations as provided by the European Copernicus Marine Services. Same as Fig. (2015) found the correlation of the frontal positions with changing atmospheric forcing related to the SAM which is noisy, and Chapman (2017) found no statistically significant frontal displacements in the south of Australia with changing SAM. Geophys Res Lett 42:81148121. Their being dark increases how much of the sun's heat they will absorb (not reflect), speeding the rate at which they melt. doi:10.1175/JPO2934.1, Hughes CW, Woodworth PL, Meredith MP, Stepanov V, Whitworth T, Pyne AR (2003) Coherence of Antarctic sea levels, Southern Hemisphere Annular Mode, and flow through Drake Passage. J Geod 90(9):807813. Google Scholar, Aoki S, Yoritaka M, Masuyama A (2003) Multidecadal warming of subsurface temperature in the Indian sector of the Southern Ocean. The question now is how this increased transfer of heat across the Antarctic Circumpolar Current will impact the stability of the Antarctic ice sheet, and consequently the rate of global sea-level rise. Nat Clim Chang 4:564569. Jul 28, 2023 7:24 PM by The sea ice extent around the antarctic continent for this day appears in light blue. Ocean Sci 8(5):859868. In the Antarctic Circumpolar Current there are sharp changes in water density known as fronts. Explainer: how the Antarctic Circumpolar Current helps - CSIROscope 2c, 20032015. (PDF) The Antarctic Circumpolar Current system - ResearchGate d The red curves are the u profiles along cross sections AA, BB and CC in the eastern hemisphere in b, and the black curves are the same w.r.t. Cambridge University Press, New York, p 323, Nowlin WD Jr, Klinck JM (1986) The physics of the Antarctic circumpolar current. The Antarctic Circumpolar Current carries an estimated 165 million to 182 million cubic meters of water every second (a unit also called a Sverdrup) from west to east, more than 100 times the flow of all the rivers on Earth. https://www.google.com.au/amp/s/theconversation.com/amp/the-air-above-antarctica-is-suddenly-getting-warmer-heres-what-it-means-for-australia-123080. Surprisingly, this has not translated into an increase in the strength of the Antarctic Circumpolar Current. 2a, b, here both being highly correlated with the SAM. The Maritime Executive. Moreover, the fact that the ACC variation keeps close pace with the SAM can be construed as evidence pronouncing that the influence largely originates from the surface by barotropic processes, as opposed to the baroclinic processes. To highlight this overall behavior change of u over the two time segments, we plot in Fig. doi:10.1029/RG024i003p00469, Olbers D, Borowski D, Vlker C, Wlff JO (2004) The dynamical balance, transport and circulation of the Antarctic circumpolar current. J Clim 15:30433057. doi:10.1002/2015GL065730, Lombard A, Garcia D, Ramillien G, Cazenave A, Biancale R, Lemoine JM, Flechtner F, Schmidt R, Ishii M (2007) Estimation of steric sea level variations from combined GRACE and Jason-1 data. doi:10.1029/2004GL019779, Thompson DWJ, Wallace JM (2000) Annular modes in the extratropical circulation. 4b) where the maximum variation u coincides with the southern or poleward rim of the ACCs main stream. The Antarctic Is Signaling Big Climate Trouble. - The New York Times We calculate the EOF for the GAD+GSM OBP anomaly in the same manner as above but separated into two ~7-year time segments: January 2003December 2009 and January 2009July 2015. 1998; Chao 2005, 2016) such as in the oceans, the TVG can be converted directly into the variation of OBP: (Wahr et al. The Antarctic Circumpolar Current (ACC) is the most important current in the Southern Ocean, and the only current that flows completely around the globe. In addition, the researchers used satellite measurements of sea surface height. 2c. The data obtained from the buoys allowed researchers to determine the velocity of the upper layer of the Southern Ocean for the first time. Nature Climate Change, 2021; DOI: 10.1038/s41558-021-01212-5, Svalbard A society in process and paradox, A sea lily snatches a ride on a crab in the Svalbard fjords, A new airline operator for Antarctica gets ready, Department of Defense, citing critical mineral needs, boosts Nome-area graphite mining project. Center for Space Research Publication, University of Texas at Austin. Variation of Antarctic circumpolar current and its intensification in relation to the southern annular mode detected in the time-variable gravity signals by GRACE satellite, $$P(\theta , \, \lambda , \, t) = \frac{{Rg\rho_{\textit{ave}} }}{3}\sum\limits_{l = 2}^{60} {\frac{2l + 1}{{1 + k_{l}^{\prime } }}\sum\limits_{m = 0}^{l} {P_{\textit{lm}} ({ \cos }\;\theta )(\Delta C_{\textit{lm}} (t)\;{ \cos }\;m\lambda + \Delta S_{\textit{lm}} (t)\;{ \sin }\;m\lambda )} }$$, $$P\left( t \right) = a + bt + ct^{2} + \alpha_{1} \;{ \sin }\omega t + \beta_{1} \;{ \cos }\omega t + \alpha_{2} \;{ \sin }2\omega t + \beta_{2} \;{ \cos }2\omega t\; + \;\hbox{``residual}\;\Delta P\left( t \right)\hbox{''}.$$, $$\Delta u = - \frac{1}{{\rho_{w} f}}\frac{{\partial {\kern 1pt} \Delta P}}{\partial y},\;\Delta v = \frac{1}{{\rho_{w} f}}\frac{{\partial {\kern 1pt} \Delta P}}{\partial x}$$, \(g\int_{ - h}^{0} {\Delta \rho {\text{d}}z}\), https://doi.org/10.1186/s40623-017-0678-3, ftp://podaac.jpl.nasa.gov/allData/grace/docs/TN-07_C20_SLR.txt, 10.1175/1520-0442(2002)015<3043:SVITSH>2.0.CO;2, 10.1175/1520-0442(2003)016<4134:TITSAM>2.0.CO;2, 10.1175/1520-0442(2000)013<3599:RBLFVI>2.0.CO;2, 10.1175/1520-0485(1993)023<0776:OTTAAM>2.0.CO;2, 10.1175/1520-0442(2000)013<1000:AMITEC>2.0.CO;2, http://creativecommons.org/licenses/by/4.0/. Assuming that the mass redistribution (that are of interest here) only occurs on the Earth surface (Wahr et al. It is also changing as the worlds climate warms. The formation of dense Antarctic Bottom Water (AABW) and its export northward from the Antarctic continent is one of the key components of the global ocean overturning circulation, and plays a critical role in regulating Earth's climate on multi-decadal-to-millennial time scales. The Antarctic Circumpolar Current is created by the combined effects of strong westerly winds across the Southern Ocean, and the big change in surface temperatures between the Equator and the poles. 4b, c, a strong variability of the anomaly u is evident, namely a clockwise shift of the most intensive portion of the ACC u variation along the whole eastern hemispheric coast. Cite this article. Our analysis essentially follows the same approach in processing the GRACE TVG observations. The drilling locations varied in water depth between ~1000 to 3900 meters. statement and Note that removing the quadratic term practically removes the dominant trending signals of land-ice mass depletion/growth on the Antarctica (including their leakages to the ocean area), as well as possible non-surficial effect of the post-glacier rebound TVG so that the conversion of the TVG to the OBP (Eq. The Antarctic Circumpolar Current - Miami Is Atlantic Ocean current near collapse? Could be sooner than expected It should be pointed out that this variation, controlling the entire ocean area where the ACC resides, represents one dominant meteorological signal that is actually not captured by the present atmosphereocean general circulation models (Atmosphere and Ocean De-aliasing Level-1B products adopted by the GRACE project to yield the GAD data and removed from the GRACE observations as stated). Kathryn Hansen/NASA We particularly thank the assistance of the summer intern students Ya-Min Yang, Ya-Ting Tsui and Wan-Hsin Yang. The DYNAPACC scientists are testing two major scientific hypotheses. Published 2008). By contrast, the GRACE TVG signals are indifferent to the state of the floating sea ice. Antarctic: Ocean Circulation - Dive & Discover The Southern Ocean has warmed and freshened in the upper 2,000 meters. For one thing, the present results suffer considerably less from the striping noise. The Maritime Executive. doi:10.1002/joc.1499, Hogg AMcC, Blundell JR (2006) Interdecadal variability of the Southern Ocean. The Antarctic Circumpolar Current, or ACC, is the strongest ocean current on our planet and is vital for Earths health because it keeps Antarctica cool and frozen. The main dataset GSM is the GRACE-observed TVG upon the removal of the GAD (Flechtner 2007). doi:10.1175/1520-0442(2002)015<3043:SVITSH>2.0.CO;2, Hannachi A, Jolliffe IT, Stephenson DB (2007) Review empirical orthogonal functions and related techniques in atmospheric science: a review. PubMedGoogle Scholar. Benoit Legresy is affiliated with the CSIRO. Dynamics of Pacific Antarctic Circumpolar Current (DYNAPACC) These pathways are the main way that the oceans absorb heat and carbon dioxide and sequester it in the deep ocean. We calculate the empirical orthogonal functions (EOF) of the non-seasonal ocean bottom pressure (OBP) field in the circum-Antarctic seas from the GRACE data for the period from 2003 to 2015. The Antarctic Circumpolar Current (ACC) is the largest oceanic current system on Earth 1. J Clim 27(4):14451468. A positive SAM Index (on the right panel) means the stronger westerly wind, the faster ACC, the Ekman transport anomaly moving toward the equator, and the sea level increasing (decreasing) away from (toward) the Antarctica. For example, in the positive phase of the SAM, the region of the largest westerly surface wind stress shifts poleward giving rise to a poleward intensification of the ACC, which in turn enhances the equatorward Ekman transport across the ACC (Hall and Visbeck 2002). 20 (Cheng and Ries 2008) and we apply two spatial filters sequentially to reduce the NS striping and high-wave-number noises in the GRACE GSM data, namely a decorrelation filter using the same empirical parameters as their result (Duan et al. 2004) has been observing the time-variable gravity (TVG) data for the study of mass transports occurring on or in the Earth. Unlike previous studies, the team led by Jia-Rui Shi, post-doctoral researcher at Woods Hole Oceanographic Institution, Massachusetts, and lead author of the study, was able to use a global network of Argo measuring buoys for their investigations, which have also been drifting in the Antarctic Circumpolar Current (ACC) since 2005. The spatial pattern of the zonal component anomaly u thus derived is plotted in Fig. (2011) reported a GRACE finding of a record increase of ocean bottom pressure (OBP) in the southeast Pacific during late 2009. Additional file 1. We love hearing from you, but we have a few guidelines. (2008) estimated that the geocenter has maximum annual amplitude of about 14mm, while the non-seasonal standard deviation is much less at ~0.9mm. Antarctic Circumpolar Current picking up speed | Polarjournal It is vital for. ftp://podaac.jpl.nasa.gov/allData/grace/docs/TN-07_C20_SLR.txt, Duan XJ, Guo JY, Shum CK, van der Wal W (2009) On the postprocessing removal of correlated errors in GRACE temperal gravity field solutions. The Antarctic Circumpolar Current carries an estimated 165 million to 182 million cubic meters of water every second (a unit also called a "Sverdrup") from west to east, more than 100 times . doi:10.1016/j.jog.2013.08.005, Flechtner F (2007) AOD1B Product Description Document for Product Releases 01 to 04. The second hypothesis being tested is if variations in the interaction of the Southern Pacific Ocean with the ACC are what determine the physical and biological characteristics of the oceanic carbon pump which helps to regulate atmospheric CO, . Top stories emailed to your inbox each day! doi:10.1029/2010GL046013, Bning CW, Dispert A, Visbeck M, Rintoul SR, Schwarzkopf FU (2008) The response of the Antarctic Circumpolar Current to recent climate change. High correlation is again found between the EOF time series and the SAM Index: The correlation coefficient is 0.66 at zero time shifts, far exceeding, say, the 0.1% significant level of 0.27 given the pertinent degree of freedom of the broadband GSM data. There are 16 missing months (June 2003, January 2011, June 2011, November 2011, December 2011, April 2012, May 2012, October 2012, March 2013, August 2013, September 2013, February 2014, July 2014, December 2014, May 2015 and June 2015) from the datasets; the moderate data gaps, however, pose no computational obstacles to our analysis which does not insist on equally spaced data. doi:10.1175/JPO3009.1. The region has lots of upwelling - very "rich" ocean basin (nutrients for plankton; food for higher-level feeders) J Geophys Res 117:C05044. 1 Investigation of the role of ocean heat in this change illuminates a number of fundamental insights regarding the important role of the Antarctic Circumpolar Current (ACC) in this and all other aspects of the Antarctic ice system. Antarctic circumpolar current's role in the Antarctic ice system: An We take the GRACE Level-2 Release-05 TVG data provided by the CSR (Center for Space Research, University of Texas), altogether 139 monthly global maps spanning a total of 12.5years from January 2003 to July 2015. It flows in a clockwise direction around Antarctica, interacting with the Atlantic, Indian, and Pacific oceans along the way. The first is to determine if the dynamics of the ACC flowing through the Drake Passage has impacted the overturning of the ocean circulation. Antarctica is the only continent that has an ocean current circulating completely around it. For decades, climate change has proceeded at roughly the expected pace, says David Armstrong McKay, a climate scientist at the University of Exeter, in England. 4a are on the order of 5-10mm/s, which, again, are numerically subdued values upon the smoothing and filtering of the GRACE data as described above. 2008) compared 5years of the early GRACE data with in situ observations and numerical model simulations and found the ACC correlation with the SAM. The ACC also plays a part in the meridional (or global) overturning circulation, which brings deep waters formed in the North Atlantic southward into the Southern Ocean. For instance, denser waters sit lower and lighter waters stand taller, and differences between the height of the sea surface give the speed of the current. The ACC, as it encircles the Antarctic continent, flows eastward through the southern portions of the Atlantic, Indian, and Pacific Oceans. Orbital- and millennial-scale Antarctic Circumpolar Current variability The Maritime Executive. J Phys Oceanogr 23:776782. Our aim is to demonstrate the utility of the satellite TVG data in providing independent observations toward better understanding of the target oceanographic processes. The inset illustrates the two processes that increase the density: lowering the . J Geodynamics 39(3):223230. Int J Climatol 27(9):11191152. Geophys Res Lett 38(4):L04602. No significant correlation is seen in the other higher EOF mode time series with the SAM Index, see Additional file 1 (In passing, we have also done the same for the dataset GAC+GSM, where the GAC is just like the GAD but not excluding the land areas.
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