Progress of Chinese research in physical oceanography of the Southern Ocean

Oceanographic surveying has been one of the key missions of the Chinese National Antarctic Research Expedition since 1984. Using the field data obtained in these surveys and the results from remote sensing and numerical models, Chinese physical oceanographers have investigated the water masses, fronts and circulation patterns in the Southern Ocean. The results of nearly 30 years of research are summarized in this paper. Most oceanographic observations by Chinese researchers have been conducted in Prydz Bay and the adjacent seas. CTD (Conductivity Temperature and Depth) data, collected during the past 20 years, have been applied to study several features of the water masses in this region: The spatial variation of warm summer surface water, the northward extension of shelf water, the flow of ice shelf water from the cavity beneath the Amery Ice Shelf, the upwelling of the Circumpolar Deep Water, and the formation of the Antarctic Bottom Water. The circulation and its dynamic factors have been analyzed with dynamic heights calculated from CTD data as well as by numerical models. The structure and strength of the fronts in the southeast Indian Ocean and the Drake Passage were investigated with underway XBT/XCTD (Expendable Bathythermograph/ Expendable CTD) and ADCP (Acoustic Doppler Current Profiler) data. Their interannual variations have been determined and the factors of influence, especially the atmospheric forcing and mesoscale oceanic processes, were studied using remote sensing data. The dynamic mechanism of the Antarctic Circumpolar Current (ACC) was analyzed by theoretical models. The transport and pattern of the ACC have been well reproduced by coupled sea ice-ocean models. Additional details of ACC variability were identified based on satellite altimeter data. The response of the ACC to climate change was studied using reanalysis data. Prospects for future research are presented at the end of this paper

Numerical simulation of the dynamic effects of grounding icebergs on summer circulation in Prydz Bay, Antarctica

The Regional Ocean Modeling System (ROMS) is employed to create a three-dimensional numerical model of the summer circulation in the Prydz Bay region, Antarctica. Consistent with the currents measured using an underway acoustic Doppler current profiler during a Chinese cruise, the simulated current field illustrates the major features of the Prydz Bay circulation, including the Antarctic Slope Current (ASC) along the continental shelf break, the cyclonic Prydz Bay Gyre, and the Prydz Bay Eastern Coastal Current (PBECC). The effects of grounding icebergs D15 and B15 on the circulation in Prydz Bay are investigated via numerical simulations. The results indicate that these giant grounding icebergs substantially affect the flows into and within the bay, which may differ with the different grounding locations. As grounding iceberg D15 is located close to the southwestern part of the West Ice Shelf (WIS), it cuts off the coastal current along the outer edge of the WIS, and the ASC can only enter Prydz Bay from the west side of iceberg D15, whereupon it becomes a main source of the PBECC. Iceberg D15 also weakens the circulation in the bay in general. The relatively small iceberg B15 entered Prydz Bay from 2007 to 2009 and grounded on the southwestern section of the Four Ladies Bank. The numerical experiments indicate that iceberg B15 guides the ASC flowing into the bay around its west side and reduces the width of the inflow on the eastern side of the Prydz Bay Channel. The grounding of iceberg B15 has also led to adjustments of the circulation within the bay, among which the most significant is that the outflow along the western flank of Fram Bank has shifted to the west and become more intensive

Chinese investigation and research in Southern Ocean physical oceanography and meteorology during the Chinese Polar Programs 2011–2015

Within the context of developing a research presence in the Antarctic region, the first phase of the Chinese Polar Programs covered the period 2011–2015, which almost coincided with the 12th Five-Year Plan (2011–2015). For the promotion of full understanding of the progress of Chinese expeditions and research in Antarctica, the observations and achievements of cruises during 2011–2015 are summarized in this paper. Four Antarctic cruises (28th–31st) were performed in the Prydz Bay and Antarctic Peninsula regions during the first phase of the Polar Programs. These cruises performed systemic collections of physical oceanographic and meteorological data to support further research on the ice–ocean–atmosphere interactions in Antarctica. Overall, 248 CTD/LADCP stations, 66 microstructure profiles, 507 XBT/XCTDs, 181 air sounding balloons, 58000 total gaseous mercury (TGM) concentrations, 452 aerosol samples, 294 atmospheric samples, 11 moorings, and 28 surface drifters were acquired or deployed during the four cruises. Using these extensive observations and other data, Chinese scientists have achieved new recognition in the fields of Southern Ocean physical oceanography and meteorology, as well as in other interdisciplinary subjects. These studies, which have been associated with scientific techniques, instrumentation, ocean circulation, water mass formation, energy transformation, and carbon uptake, have elucidated the dynamic mechanisms and potential effects of climate change in Antarctica. Finally, some observations based on experience gained during previous Chinese Antarctic Research and Expedition campaigns are summarized with advice for the improvement of future investigations in the Antarctic region

Summer freshwater content variability of the upper ocean in the Canada Basin during recent sea ice rapid retreat

Freshwater content (FWC) in the Arctic Ocean has changed rapidly in recent years, in response to significant decreases in sea ice extent. Research on freshwater content variability in the Canada Basin, the main storage area of fresh water is very important to understand the input-output freshwater in the Arctic Ocean. The FWC in the Canada Basin was calculated using data from the Chinese National Arctic Research Expeditions of 2003 and 2008, and from expeditions of the Canadian icebreaker Louis S. St-Laurent (LSSL) from 2004 to 2007. Results show that the upper ocean in the Canada Basin became continuously fresher from 2003 to 2008, except during 2006. The FWC increased at a rate of more than 1 m¢a¡1, and the maximum increase, 7 m, was in the central basin compared between 2003 and 2008. Variability of the FWC was almost entirely limited to the layer above the winter Bering Sea Water (wBSW), below which the FWC remained around 3 m during the study period. Contributors to the FWC increase are generally considered to be net precipitation, runoff changes, Pacific water inflow through the Bering Strait, sea ice extent, and the Arctic Oscillation(AO). However, we determined that the first three contributors did not have apparent impact on the FWC changes. Therefore, this paper focuses on analysis of the latter two factors and the results indicate that they were the major contributors to the FWC variability in the basin

Persistent warm-eddy transport to Antarctic ice shelves driven by enhanced summer westerlies

The offshore ocean heat supplied to the Antarctic continental shelves by warm eddies has the potential to greatly impact the melting rates of ice shelves and subsequent global sea level rise. While featured in modeling and some observational studies, the processes around how these warm eddies form and overcome the dynamic sub-surface barrier of the Antarctic Slope Front over the upper continental slope has not yet been clarified. Here we report on the detailed observations of persistent eddies carrying warm modified Cir- cumpolar Deep Water (CDW) onto the continental shelf of Prydz Bay, East Antarctica, using subsurface mooring and hydrographic section data from 2013-2015. We show the warm-eddy transport is most active when the summer westerlies strengthen, which promotes the upwelling of CDW and initiates eddy formation and intrusions. Our study highlights the important role of warm eddies in the melting of Antarctica’s ice shelves, both now and into the future. Keywords: Antarctic Deep Water, ocean heat, warm eddie

Overview of China’s Antarctic research progress 1984–2016

It is more than 30 years since the first Chinese National Antarctic Research Expedition (CHINARE) landed in Antarctica in 1984, representing China’s initiation in polar research. This review briefly summarizes the Chinese Antarctic scientific research and output accomplished over the past 30 years. The developments and progress in Antarctic research and the enhancement of international scientific cooperation achieved through the implementation of the CHINARE program have been remarkable. Since the 1980s, four permanent Chinese Antarctic research stations have been established successively and 33 CHINAREs have been completed. The research results have been derived from a series of spatiotemporal observations in association with various projects and multidisciplinary studies in the fields of oceanography, glaciology, geology, geophysics, geochemistry, atmospheric science, upper atmospheric physics, Antarctic astronomy, biology and ecology, human medicine, polar environment observation, and polar engineering

Delivering sustained, coordinated and integrated observations of the Southern Ocean for global impact

The Southern Ocean is disproportionately important in its effect on the Earth system, impacting climatic, biogeochemical, and ecological systems, which makes recent observed changes to this system cause for global concern. The enhanced understanding and improvements in predictive skill needed for understanding and projecting future states of the Southern Ocean require sustained observations. Over the last decade, the Southern Ocean Observing System (SOOS) has established networks for enhancing regional coordination and research community groups to advance development of observing system capabilities. These networks support delivery of the SOOS 20-year vision, which is to develop a circumpolar system that ensures time series of key variables, and delivers the greatest impact from data to all key end-users. Although the Southern Ocean remains one of the least-observed ocean regions, enhanced international coordination and advances in autonomous platforms have resulted in progress toward sustained observations of this region. Since 2009, the Southern Ocean community has deployed over 5700 observational platforms south of 40°S. Large-scale, multi-year or sustained, multidisciplinary efforts have been supported and are now delivering observations of essential variables at space and time scales that enable assessment of changes being observed in Southern Ocean systems. The improved observational coverage, however, is predominantly for the open ocean, encompasses the summer, consists of primarily physical oceanographic variables, and covers surface to 2000 m. Significant gaps remain in observations of the ice-impacted ocean, the sea ice, depths >2000 m, the air-ocean-ice interface, biogeochemical and biological variables, and for seasons other than summer. Addressing these data gaps in a sustained way requires parallel advances in coordination networks, cyberinfrastructure and data management tools, observational platform and sensor technology, two-way platform interrogation and data-transmission technologies, modeling frameworks, intercalibration experiments, and development of internationally agreed sampling standards and requirements of key variables. This paper presents a community statement on the major scientific and observational progress of the last decade, and importantly, an assessment of key priorities for the coming decade, toward achieving the SOOS vision and delivering essential data to all end-users.Fil: Newman, Louise. University of Tasmania; AustraliaFil: Heil, Petra. Australian Antarctic Division; Australia. Antarctic Climate And Ecosystems Cooperative Research Centre; AustraliaFil: Trebilco, Rowan. Australian Antarctic Division; Australia. Antarctic Climate And Ecosystems Cooperative Research Centre; AustraliaFil: Katsumata, Katsuro. Japan Agency For Marine earth Science And Technology; JapónFil: Constable, Andrew J.. Antarctic Climate And Ecosystems Cooperative Research Centre; Australia. Australian Antarctic Division; AustraliaFil: Wijk, Esmee van. Commonwealth Scientific And Industrial Research Organization; Australia. Antarctic Climate And Ecosystems Cooperative Research Centre; AustraliaFil: Assmann, Karen. University Goteborg; SueciaFil: Beja, Joana. British Oceanographic Data Centre; AustraliaFil: Bricher, Phillippa. University of Tasmania; AustraliaFil: Coleman, Richard. University of Tasmania; AustraliaFil: Costa, Daniel. University of California; Estados UnidosFil: Diggs, Steve. University of California; Estados UnidosFil: Farneti, Riccardo. The Abdus Salam; Italia. The Abdus Salam. International Centre for Theoretical Physics; ItaliaFil: Fawcett, Sarah. University of Cape Town; SudáfricaFil: Gille, Sarah. University of California; Estados UnidosFil: Hendry, Katharine R.. University of Bristol; Reino UnidoFil: Henley, Sian F.. University of Edinburgh; Reino UnidoFil: Hofmann, Eileen. Old Dominion University; Estados UnidosFil: Maksym, Ted. University of California; Estados UnidosFil: Mazloff, Matthew. University of California; Estados UnidosFil: Meijers, Andrew J.. British Antartic Survey; Reino UnidoFil: Meredith, Michael. British Antartic Survey; Reino UnidoFil: Moreau, Sebastien. Norwegian Polar Institute; NoruegaFil: Ozsoy, Burcu. Istanbul Teknik Üniversitesi; TurquíaFil: Robertson, Robin. Xiamen University; ChinaFil: Schloss, Irene Ruth. Universidad Nacional de Tierra del Fuego; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; ArgentinaFil: Schofield, Oscar. State University of New Jersey; Estados UnidosFil: Shi, Jiuxin. Ocean University Of China; ChinaFil: Sikes, Elisabeth L.. State University of New Jersey; Estados UnidosFil: Smith, Inga J.. University of Otago; Nueva Zeland

Variability and Formation Mechanism of Polynyas in Eastern Prydz Bay, Antarctica

Based on satellite remote sensing, several polynyas have been found in Prydz Bay, East Antarctica. Compared with the Mackenzie Bay Polynya, the only polynya in the west, the polynyas in eastern Prydz Bay have a larger area and higher ice production, but have never been studied individually. In this study, four recurrent polynyas were identified in eastern Prydz Bay from sea ice concentration data during 2002–2011. Their areas generally exhibit synchronous temporal variations and have good correlation with wind speed, which indicates that they are primarily wind-driven polynyas that need at least one stationary ice barrier to block the inflow of drifting sea ice. The components of the ice barriers of these four polynyas were identified through comparison of satellite remote sensing visible images and synthetic aperture radar images. All types of fast ice, including landfast ice, offshore fast ice and ice fingers serving as ice barriers for these polynyas are anchored by an assemblage of small icebergs and have an approximately year-round period of variations that also regulates the variability of polynyas. The movement and grounding of giant icebergs near the polynyas significantly affects the development of the polynyas. The results of this study illustrate the important impact of icebergs on Antarctic wind-driven polynyas and the formation of dense shelf water

A sub-surface eddy at inertial current layer in the Canada Basin, Arctic Ocean

An Arctic Ocean eddy in sub-surface layer is analyzed in this paper by use of temperature, salinity and current profiles data obtained at an ice camp in the Canada Basin during the second Chinese Arctic Expedition in summer of 2003. In the vertical temperature section, the eddy show itself as an isolated cold water block at depth of 60m with a minimum temperature of -1.5°C, about 0.5°C colder than the ambient water. Isopycnals in the eddy form a pattern of convex, which indicates the eddy is anticyclonic. Although maximum velocity near 0.4m s(-1) occurs in the current records observed synchronously, the current pattern is far away from a typical eddy. By further analysis, inertial frequency oscillations with amplitudes comparable with the eddy velocity are found in the sub-surface layer currents. After filter the inertial current and mean current, an axisymmetric current pattern of an eddy with maximum velocity radius of 5km is obtained. The analysis of the T-S characteristics of the eddy core water and its ambient waters supports the conclusion that the eddy was formed on the Chukchi Shelf and migrated northeastward into the northern Canada Basin