ORCID Profile
0000-0003-3631-5365
Current Organisations
University of Tasmania
,
ARC Australian Centre for Excellence in Antarctic Science (ACEAS)
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Publisher: Elsevier BV
Date: 02-2023
Publisher: American Geophysical Union (AGU)
Date: 11-09-2023
DOI: 10.1029/2022GL097864
Publisher: Wiley
Date: 07-02-2022
Publisher: American Association for the Advancement of Science (AAAS)
Date: 11-06-2021
Abstract: Poleward expansion of the Antarctic Circumpolar Current warms the Antarctic continental margin.
Publisher: American Geophysical Union (AGU)
Date: 08-2020
DOI: 10.1029/2019JC015406
Publisher: Springer Science and Business Media LLC
Date: 15-09-2020
DOI: 10.1038/S41598-020-71290-6
Abstract: The Antarctic continental margin supplies the densest bottom water to the global abyss. From the late twentieth century, an acceleration in the long-term freshening of Antarctic Bottom Waters (AABW) has been detected in the Australian-Antarctic Basin. Our latest hydrographic observations reveal that, in the late 2010s, the freshening trend has reversed broadly over the continental slope. Near-bottom salinities in 2018–2019 were higher than during 2011–2015. Along 170° E, the salinity increase between 2011 and 2018 was greater than that observed in the west. The layer thickness of the densest AABW increased during the 2010s, suggesting that the Ross Sea Bottom Water intensification was a major source of the salinity increase. Freshwater content on the continental slope decreased at a rate of 58 ± 37 Gt/a in the near-bottom layer. The decadal change is very likely due to changes in Ross Sea shelf water attributable to a decrease in meltwater from West Antarctic ice shelves for the corresponding period.
Publisher: American Geophysical Union (AGU)
Date: 27-12-2021
DOI: 10.1029/2021JC017953
Abstract: To quantitatively assess the inorganic carbon cycle in the eastern Indian sector of the Southern Ocean (80–150°E, south of 60°S), we measured ocean surface temperature, salinity, total alkalinity (TA), the partial pressure of carbon dioxide (pCO 2 ), and concentrations of chlorophyll‐ a (chl a ), dissolved inorganic carbon (DIC), and nutrients during the KY18 survey (December 2018–January 2019). The sea–air CO 2 flux in this region was −8.3 ± 12.7 mmol m −2 day −1 (−92.1 to +10.6 mmol m −2 day −1 ). The ocean was therefore a weak CO 2 sink. Based on the DIC and TA in the temperature minimum layer, we estimated the change of pCO 2 from winter to summer (δpCO 2 ) due to changes in water temperature, salinity, and biological activity (photosynthesis). The spatial distribution of pCO 2 in the western part (80–110°E) of the study area was mainly driven by biological activity, which decreased pCO 2 from December to early January, and in the eastern part (110–150°E) by temperature, which increased pCO 2 from January to February. We also examined the changes in the CO 2 concentrations (xCO 2 ) over time by comparing data from 1996 with our data (2018–2019). The oceanic and atmospheric xCO 2 increased by 23 and 45 ppm in 23 years, respectively. These changes of ocean xCO 2 were mainly driven by an increase in CO 2 uptake from the atmosphere as a result of the rise in atmospheric xCO 2 and increase in biological activity associated with the change in the water‐mass distribution.
Publisher: American Geophysical Union (AGU)
Date: 02-2023
DOI: 10.1029/2022JC019422
Abstract: Warm, salty Circumpolar Deep Water (CDW) is recognized as the primary driver for Antarctic glacial melt, but the mechanism by which it reaches the continental shelves remains highly uncertain from an observational standpoint. With the scarcity of eddy flux estimation in the Antarctic margin, we quantify the isopycnal diffusivity of CDW using hydrographic variability and satellite altimetry under the mixing length framework. For comparison, the spiciness and thickness are used as isopycnal tracers, and the two tracers yield qualitatively similar estimates. Over the Antarctic Circumpolar Current (ACC), variation of mixing length is generally aligned with the jet‐induced mixing suppression, including in areas where topography blocks the jet's influence. In contrast, the mixing length does not depend on the mean flow in the subpolar zone, likely reflecting the relatively quiescent flow regime. The estimated isopycnal diffusivity ranges from 100 to 500 m 2 s −1 south of the ACC. The eddy diffusivity tends to be enhanced where the gradient of isopycnal thickness becomes small and CDW intrudes onshore. The cross‐slope eddy CDW flux is estimated, and the associated onshore heat flux across is calculated as ∼3.6 TW in the eastern Indian sector. The eddy heat flux and coastal solar heating are generally balanced with cryospheric heat sinks including glacial melting and surface freezing, suggesting that the eddy advection is substantial for the onshore CDW flux. The thickness field is essential for determining mixing length and eddy fluxes in the subpolar zone, however this is not the case in the ACC domain.
Publisher: Wiley
Date: 27-10-2022
Publisher: Springer Science and Business Media LLC
Date: 08-06-2021
DOI: 10.1038/S41598-021-91412-Y
Abstract: The interbasin exchange between the Sea of Okhotsk and the North Pacific governs the intermediate water ventilation and fertilization of the nutrient-rich subpolar Pacific, and thus has an enormous influence on the North Pacific. However, the mechanism of this exchange is puzzling current studies have not explained how the western boundary current (WBC) of the subarctic North Pacific intrudes only partially into the Sea of Okhotsk. High-resolution models often exhibit unrealistically small exchanges, as the WBC overshoots passing by deep straits and does not induce exchange flows. Therefore, partial intrusion cannot be solely explained by large-scale, wind-driven circulation. Here, we demonstrate that tidal forcing is the missing mechanism that drives the exchange by steering the WBC pathway. Upstream of the deep straits, tidally-generated topographically trapped waves over a bank lead to cross-slope upwelling. This upwelling enhances bottom pressure, thereby steering the WBC pathway toward the deep straits. The upwelling is identified as the source of joint-effect-of-baroclinicity-and-relief (JEBAR) in the potential vorticity equation, which is caused by tidal oscillation instead of tidally-enhanced vertical mixing. The WBC then hits the island chain and induces exchange flows. This tidal control of WBC pathways is applicable on subpolar and polar regions globally.
Publisher: Springer Science and Business Media LLC
Date: 22-06-2022
DOI: 10.1038/S43247-022-00456-Z
Abstract: Melting ice shelves around Antarctica control the massive input of freshwater into the ocean and play an intricate role in global heat redistribution. The Amery Ice Shelf regulates wintertime sea-ice growth and dense shelf water formation. We investigated the role of warm Antarctic Surface Water in ice shelf melting and its impact on dense shelf water. Here we show that the coastal ocean in summer 2016/17 was almost sea-ice free, leading to higher surface water temperatures. The glacial meltwater fraction in surface water was the highest on record, hypothesised to be attributable to anomalous ice shelf melting. The excess heat and freshwater in early 2017 delayed the seasonal evolution of dense shelf water. Focused on ice shelf melting at depth, the importance and impacts of warming surface waters has been overlooked. In a warming climate, increased surface water heating will reduce coastal sea-ice production and potentially Antarctic Bottom Water formation.
Publisher: Wiley
Date: 28-01-2022
Publisher: Elsevier BV
Date: 09-2023
Publisher: American Geophysical Union (AGU)
Date: 09-2023
DOI: 10.1029/2022GB007510
Abstract: To clarify the impacts of basal melting of the Antarctic ice sheet and biological productivity on biogeochemical processes in Antarctic coastal waters, concentrations of dissolved inorganic carbon (DIC), total alkalinity (TA), inorganic nutrients, chlorophyll a , and stable oxygen isotopic ratios (δ 18 O) were measured from the offshore slope to the ice front of the Totten Ice Shelf (TIS) during the spring/summer of 2018, 2019, and 2020. Modified Circumpolar Deep Water (mCDW) intruded onto the continental shelf off the TIS and flowed along bathymetric troughs into the TIS cavity, where it formed a buoyant mixture with glacial meltwater from the ice shelf base. Physical oceanographic processes mostly determined the distributions of DIC, TA, and nutrient concentrations. However, photosynthesis and dilution by meltwater from sea ice and the ice shelf base decreased DIC, TA, and nutrient concentrations in surface water near the ice front. These causes also reduced the CO 2 partial pressure in surface water by more than 100 μatm with respect to mCDW in austral summer of 2018 and 2020, and the surface water became a strong CO 2 sink for the atmosphere. Phytoplankton photosynthesis changed DIC and TA in a molar ratio of 106:16. Thus, CO 2 partial pressure decreased mostly as a result of photosynthesis while dilution by glacial and sea ice meltwater had a small effect. The nutrient consumption ratio suggested that photosynthesis was stimulated by iron in the water column, supplied to the surface layer via buoyancy‐driven upwelling and basal ice shelf meltwater in addition to sea ice meltwater.
Publisher: Springer Science and Business Media LLC
Date: 17-08-2023
DOI: 10.1038/S41467-023-39764-Z
Abstract: The Totten Glacier in East Antarctica, with an ice volume equivalent to .5 m of global sea-level rise, is grounded below sea level and, therefore, vulnerable to ocean forcing. Here, we use bathymetric and oceanographic observations from previously uns led parts of the Totten continental shelf to reveal on-shelf warm water pathways defined by deep topographic features. Access of warm water to the Totten Ice Shelf (TIS) cavity is facilitated by a deep shelf break, a broad and deep depression on the shelf, a cyclonic circulation that carries warm water to the inner shelf, and deep troughs that provide direct access to the TIS cavity. The temperature of the warmest water reaching the TIS cavity varies by ~0.8 °C on an interannual timescale. Numerical simulations constrained by the updated bathymetry demonstrate that the deep troughs play a critical role in regulating ocean heat transport to the TIS cavity and the subsequent basal melt of the ice shelf.
Location: Australia
No related grants have been discovered for Kaihe Yamazaki.