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Antarctic Marine Biodiversity: Adaptations, Environments and Responses to Change
Published in S. J. Hawkins, A. J. Evans, A. C. Dale, L. B. Firth, I. P. Smith, Oceanography and Marine Biology, 2018
Temperatures of water masses vary regionally and with depth. In the Ross Sea, possibly the coldest inhabited large water mass on Earth, winter temperatures are close to the freezing point of seawater (−1.86°C) in the water column. Temperatures can be even lower than this where salinity is raised during freezing events either associated with sea ice or ice growing on the seabed close to land. In summer, temperatures in shallow water only rise to around −1.5°C (Orsi & Wiederwohl 2009). At depths below around 500 m in the Ross Sea, water temperatures are higher, up to around +1.5°C, as this is the depth that circumpolar deep water (CDW) intrudes to in this region. Circumpolar deep water is a large relatively warm saline water mass that occupies mid-water depths of the Antarctic circumpolar current. It is characteristically 2–4°C warmer than surface waters and is split into upper circumpolar deep water (UCDW) and lower circumpolar deep water (LCDW) by oceanographers.
Ocean Oscillation and Drought Indices: Principles
Published in Saeid Eslamian, Faezeh Eslamian, Handbook of Drought and Water Scarcity, 2017
Williams et al. [48] described a water mass as a large homogeneous body of water that has a particular characteristic range of temperature and salinity values. Since water masses usually gain their temperature and salinity characteristics at the surface and then seek density levels by thermohaline convection, oceanic water masses are usually characterized by both the depth at which they reach vertical equilibrium and their geographical source region. However, in the order of increasing depths, water masses may be categorized as being either surface, extending down to about 100 m; central, extending up to the base of the main thermohaline; intermediate, extending from below the central waters to about 3000 m; or deep and bottom, filling the lower portions of the ocean basin.
Trace Metals in Seawater
Published in Robert W. Furness, Philip S. Rainbow, Heavy Metals in the Marine Environment, 1990
Measures et al.44 consider that the major changes they observed in concentrations with depth are attributable to a large extent to differences in the original concentrations of the metal in source waters. They suggest that high concentrations in the Lower North Atlantic Deep Water reflect high concentrations in the upper waters north of Iceland which form the source, by convection, for this water mass. The northwestern European shelf region is suggested as the initial major source for this aluminum. The lower concentrations in the Upper North Atlantic Deep Water were considered to reflect its large component of Labrador Sea Water which has sources in Arctic surface waters that are known to be low in aluminium. In the Sargasso Sea, the signal due to Mediterranean Outflow Water, which also contributes to the Upper North Atlantic Deep Water, is weak. At its source, however, the Mediterranean Outflow Water is highly enriched in aluminum,46 probably because of dissolution from particles entering from the atmosphere; a concentration as high as 111 nmol/1 was found for the Western Mediterranean Deep Water and in the Gulf of Cadiz the Outflow water contained 72 nmol/1.
Overview of the 9th Chinese National Arctic Research Expedition
Published in Atmospheric and Oceanic Science Letters, 2020
Zexun WEI, Hongxia CHEN, Ruibo LEI, Xiaoguo YU, Tao ZHANG, Lina LIN, Zhongxiang TIAN, Yanpei ZHUANG, Tao LI, Zhuoli YUAN
Hydrographic investigations were conducted using conductivity–temperature–depth (CTD) and lowered acoustic Doppler current profiler (LADCP) sensors in the Pacific section of the Arctic Ocean. Overall, CTD/LADCP operations were performed at 88 stations during the expedition (Figure 1). Compared with historical voyage data collected during the previous CHINARE cruises from 1999 to 2012, the temperature and salinity south of the Bering Strait were slightly higher in 2018. Historical records showed a cold-water mass in the Bering Strait characterized by water temperatures of < 2°C. In-situ data from the 9th CHINARE revealed that the temperature of the water mass was > 3°C. The water mass characterized by salinity of < 32 was also markedly reduced in 2018. The physical mechanism for such moderate abnormalities of water mass is worthy of further study.
Land–sea correlations in the Australian region: 460 ka of changes recorded in a deep-sea core offshore Tasmania. Part 2: the marine compared with the terrestrial record
Published in Australian Journal of Earth Sciences, 2019
P. De Deckker, T. T. Barrows, J.-B. W. Stuut, S. van der Kaars, M. A. Ayress, J. Rogers, G. Chaproniere
Rochford (1957) identified various water masses at the surface: the Central Tasman Water [15–20 °C and in practical salinity units (PSU), 35.5–35.7], the South-west Tasman Water (SWTW) (12–15 °C, 35.25–35.4 PSU), and the North Bass Strait Water (NBSW) (12–15 °C, 35.5–35.7 PSU), which is more saline than the SWTW due to evaporation. The NBSW eventually ‘cascades’ down the Bass Canyon to dissipate northward into the Tasman Sea and is commonly referred to as a ‘Meddy’, being similar to water cascading through the Gibraltar Strait into the Atlantic Ocean (Luick, Käse, & Tomczak, 1994). At depth, the Subantarctic Intermediate Water, a mass lying between 200 and 500 m, has a lower salinity range (34.6–35.2 PSU) than the surface waters, and sits above the Antarctic Intermediate Water, which can extend down to ∼1100 m and has an even lower salinity range (34.37–34.53 PSU). The Deep Water mass extends down to ∼3000 m and has a salinity of 34.74 PSU (Supplementary papers, Figure S2). Around the Tasman Plateau, the modern thermocline is at ∼200 m water depth and the waters are depleted in silica and nitrate in the upper 100 m of the water column due to biological activity. For more information on seasonal changes of the various water masses within the upper 500 m of the water column, with respect to temperature, salinity, silica, nitrate and phosphate near the core site, see Figure S3 of Supplementary papers.
A study on the physical and biogeochemical responses of the Bay of Bengal due to cyclone Madi
Published in Journal of Operational Oceanography, 2022
Riyanka Roy Chowdhury, S. Prasanna Kumar, Arun Chakraborty
The Ekman dynamics associated with the cyclone Madi is expected to bring changes in the characteristics of the water mass prevailing in the upper ocean. To understand the changes in the water mass structure in response to cyclone Madi, T-S diagram was prepared following Ning et al. (2019a). The Box B region (see Figure 1 for the location) was chosen as it was located in the northern part of the cyclone track where the cyclone Madi interacted with the pre-existing cyclonic eddy. The box-averaged temperature vs. salinity distribution (T-S plot) was prepared using HYCOM data in the upper 200 m for 5th and 13th December which represented the pre and post-cyclone conditions respectively (Figure 7). Two water masses could be identified based on the T-S diagram such as the Bay of Bengal water mass (BoBW) and the Arabian Sea high salinity water mass (ASHSW) with the sigma-t range between 21.5–23.0 and 23.5–24.5 kg/m3 respectively (Figure 7). Prior to the cyclone Madi, the T-S curve on 5th December (red solid line) showed the presence of low salinity BoBW in the depth range of 30–75 m, while the ASHSW was just below it occupying the depth up to 125 m. After the passage of cyclone, the T-S curve on 15th December (blue solid line) showed the surfacing of the BoBW, while the ASHSW shoaled to 40 m. This clearly indicated the upper ocean response to cyclone Madi as the vertical movement of subsurface waters was facilitated by the upward Ekman pumping. This was also corroborated by the shoaling of the thermocline. The largest shift in the T-S curves occurred in the upper 125 m which was associated with the strong entrainment process. In deeper depths, both curves did not show perceptible displacement.