An optimum multiparameter mixing analysis of the shelf waters in the Ross Sea

Abstract

Abstract:The analysis of the mixing processes involving water masses on the Ross Sea continental shelf is one of the goals of the CLIMA project (Climatic Long-term Interactions for the Mass balance in Antarctica). This paper uses extended Optimum MultiParameter analysis (OMP), which is applied to four datasets collected during the cruises of 1994/95, 1995/96, 1997/98 and 2000/01 in the Ross Sea (Antarctica). Data include both hydrological, (temperature, salinity, and pressure; T, S, and P, respectively) and chemical parameters (O 2 , Si(OH) 4 , PO 4 , and NO 3 +NO 2 ). The OMP analysis is based on the assumption that the mixing is a linear process which affects all parameters equally so that each sample shows physical/chemical properties that are the result of the mixing of some properly selected Source Water Types (SWTs). OMP thus evaluates the best set of contributions by all SWTs to each sample, and allows the spatial distribution and structure of the water masses in a basin to be evaluated. Ocean circulation may subsequently be inferred by means of a deeper analysis of the spreading of the water mass. In this study, the "real" Redfield ratios observed in the Ross Sea were used to correct the equations referring to the chemical parameters in accordance with the extended version of OMP. The solutions include some physically realistic constraints. The results allow a detailed description of the water mass distribution, validated through comparison with some "canonical" thermohaline characteristics of the Ross Sea hydrology. In particular our results verify the spreading of the HSSW over the entire continental shelf and emphasize the key role it plays in the ventilation of the deep waters outside the Ross Sea. In addition a description is given of the intrusion of relatively warm waters coming from the open ocean and flowing at some specific locations at the continental shelf break. isobath, runs NW-SE and links the area in front of Cape Adare to Cape Colbeck. Some depressions in the inner area are deeper than the continental shelf break, and therefore behave as reservoirs of the salty and dense waters.The Circumpolar Deep Water (CDW) is carried by the Antarctic Circumpolar Current (ACC) along the boundary of the Ross Sea, following the shelf slope from east to west. CDW strongly influences the thermohaline circulation of this basin, being the only water mass which provides heat to the shelf waters (Jacobs et al. 1985, Locarnini 1994, Jacobs & Giulivi 1998, Gouretsky 1999. In some specific locations it intrudes onto the Ross continental shelf forming, after the interaction with the shelf waters, the modified CDW (MCDW), which can be identified by a subsurface maximum temperature and minimum dissolved oxygen (Jacobs et al. 1985, Locarnini 1994, Budillon et al. 1999.On the western side of the Ross Sea, the physical features of the water column are also affected by the recurring presence of a substantial coastal ice free area, the Terra Nova Bay polynya (Bromwich & Kurtz 1984, Jacobs et al. 1985, Fusco et al. 2...

Anthropogenic carbon distribution in the Ross Sea, Antarctica

“…The detailed description of the analysis is provided in several works (Mackas et al 1987, Tomczak & Large 1989, You & Tomczak 1993, and this kind of analysis has previously been used in the Ross Sea providing a good estimate of the mixing process and of the circulation of the different water masses (Budillon et al 2003).…”

Explicit representation and parametrised impacts of under ice shelf seas in the <i>z</i><sup>∗</sup> coordinate ocean model NEMO 3.6

“…The z * vertical coordinate can be used with a sea ice model (Campin et al, 2008) in NEMO (Madec and the NEMO team, 2016). However, modelling the ocean circulation within an ice shelf cavity in z * coordinates requires some modification of the existing code.…”

“…8). Weak winds in the atmospheric forcing , in addition to a fresher coastal current (Nakayama et al, 2014), the opening of a new pathway for HSSW circulation beneath the ice shelves (Budillon et al, 2003;Nicholls et al, 2009), mixing of HSSW with light surface waters all year long, and a deficiency of the seaice model in representing coastal polynyas could all help to explain the absence of HSSW in R_ISF.…”

“…8). In R_PAR, this is due to the lack of a HSSW circulation pathway beneath the giant Ross (Budillon et al, 2003) and Filchner-Ronne (Nicholls et al, 2009) ice shelves that in reality carries HSSW formed in the west over to the central or eastern shelf. Instead of this sub-ice shelf circulation that is captured in R_ISF (Fig.…”

Indirect investigations of the Atlantic Meridional Overturning changes in the South Atlantic Ocean in numerical models for the 20th century

“…At 11°S, the error associated with the OMP is smaller than 2% in almost all the water column analyzed (Figure 63 At 27°S, the error is smaller than 1.5% for all models. According to Budillon et al (2003), Tomczak (1981), Tomczak & Large (1989), and Frants et al (2013), the mass balance constraint is used as a measure of the uncertainty of the result and mass balance residuals of 5% or less are considered acceptable. During the empirical tests to decide the best combination of weights for the OMP analysis, it was observed that if the importance of the potential vorticity was increased, the worse (be er) the results for the SACW (AAIW), i.e., bigger (smaller) mass balance constraints.…”