Water mass census in the Nordic seas using climatological and observational data sets

We have compared and evaluated the water mass census in the Greenlend-Iceland-Norwegian (GIN) Sea area from climatologies, observational data sets and model output. The four climatologies evaluated were: the 1998 and 2001 versions of theWorld Ocean Atlas (WOA98, WOA01), and the United States Navy’s GDEM90 (Generalized Digital Environmental Model) and MODAS01 (Modular Ocean Data Assimilation System) climatologies. Three observational data sets were examined: the multidecadal (1965-1995) set contained on the National Oceanographic Data Center’s (NODC) WOD98 (World Ocean Data) CD-ROM, and two seasonal data sets extracted from observations taken on six cruises by the SACLANT Research Center (SACLANTCEN) of NATO/Italy between 1986-1989. The model data is extracted from a global model run at 1/3 degree resolution for the years 1983-1997, using the POP (Parallel Ocean Program) model of the Los Alamos National Laboratory. The census computations focused on the Norwegian Sea, in the southern part of the GIN Sea, between 10◦W-10◦E and 60◦N-70◦N, especially for comparisons with the hydrocasts and the model. Cases of such evaluation computations included: a) “short term” comparisons with quasi-synoptic CTD surveys carried out over a 4-year period in the southeastern GIN Sea; b) “climatological” comparisons utilizing all available casts from the WOD98 CD-ROM, with four climatologies; and c) a comparison between the WOA01 climatology and the POP model output ending in 1997. In this region in the spring, the fraction of ocean water that has salinity above 34.85 is ∼ 94%, and that has temperatures above 0◦C is ∼ 33%. Three principal water masses dominated the census: the Atlantic water AW, the deep water DW and an intermediate water mass defined as Lower Arctic Intermediate Water (LAIW). Besides these classes, both the climatologies and the observations exhibited the significant presence of deep water masses with T-S characteristics that do not fall into the “named” varieties, e.g., Norwegian Sea or Greenland Sea deep water (NSDW, GSDW). The seasonal volumetric changes for the Atlantic (AW), intermediate (LAIW) and deep waters (DW) in the GIN Sea are in reasonably good agreement between the climatologies, and with the results of hydrographic census surveys. Typical seasonal changes (spring-summer) involve about 30 × 103 km3 of AW increase and 33 × 103 km3 of LAIW decrease, and a decrease of about 32 × 103 km3 of DW between spring and autumn

Shelf slope convection: A note for antarctic regions

Some basic processes associated with buoyancy-driven convection in the presence of coastal upwellingcurren ts were investigated in a 2.5D framework near the Adelie Coast of Antarctica. The surface buoyancy forcingw as derived from coolingand brine deposition due to ice formation, and was specified over a persistent off-shore polynya maintained by the off-shore katabatic winds. Rotational effects and the formation of a turbulent surface mixed layer were included in the model. The representation of topography was done via the VBM (virtual Boundary Method) that utilizes equivalent body forces in the momentum equation, thus enabling the use of very efficient Poisson solvers for the pressure, based on FFTs. The simulations were carried out near longitude 143E, between latitude 68S and 65S, over the nearshore shelf region. The hydrography was initialized with the 1/4 deg Levitus annual climatology. Two cases of idealized meteorological forcing were considered: constant winds blowingalong -shore and off-shore. The resultant motions in each case were characterized by interaction between the wind-driven upwellingmotions and the downward movingdense convection plumes, but with marked differences: a) the formation of a strongfron t under the open sea edge of the polynya only by off-shore winds; b) the periodic suppression of the surface off-shore currents and of the coastal upwelling only by the along-shore winds; c) the formation of deep upwelling currents along the slope between 400 and 200 meters only for along-shore winds, and d) the rapid filling of the surface layers (depths < 100m) with high salinities under the whole polynya by the off-shore forcing, vs. the delayed fillingof a narrow region near the downwellingplume with intermediate salinity values by the along-shore forcing

Massively parallel implementation of a high order domain decomposition equatorial ocean model

The present work is about the algorithms and parallel constructs of a spectral element equatorial ocean model. It shows that high order domain decomposition ocean models can be efficiently implemented on massively parallel architectures, such as the Connection Machine Model CM5. The optimized computational efficiency of the parallel spectral element ocean model comes not only from the exponential convergence of the numerical solution, but also from the work-intensive, medium-grained, geometry-based data parallelism. The data parallelism is created to efficiently implement the spectral element ocean model on the distributed-memory massively parallel computer, which minimizes communication among processing nodes. Computational complexity analysis is given for the parallel algorithm of the spectral element ocean model, and the model's parallel performance on the CM5 is evaluated. Lastly, results from a simulation of wind-driven circulation in low-latitude Atlantic Ocean are described

Variability of trace-elements and δ18O in drip water from Gruta del Rey Marcos, Guatemala; seasonal and environmental effects, and its implications for paleoclimate reconstructions

Guatemala is located at the core of one of the largest warming pools in the planet, the Western Hemisphere Warm Pool, an important source of tropical moisture to middle and high latitudes and, thus, a key area for paleoclimatic studies. This, along the karst pervasiveness in the area provides the opportunity to obtain high-resolution records of past hydroclimatic conditions using stalagmites. Despite this, the atmospheric and geochemical processes that might affect the variability of geochemical proxies in stalagmites are yet to be constrained, as no cave-monitoring in the area has been carried out previously. Here, we present a 2.5-year cave-monitoring study from Gruta del Rey Marcos, Guatemala, which allows to understand the effect of external atmospheric and environmental conditions upon the variability of δ18O, Mg/Ca, Sr/Ca, and Ba/Ca in drip water. By incorporating cave ventilation dynamics, isotopic information of local rainfall and cave-river water, we are able to understand the most relevant processes that affect the variability of the geochemical proxies in drip water, hence stalagmites. Our results suggest that two-isotopically distinct rainfall regimes, as well as tropical cyclones affecting the area contribute to the composition of the drip-water, hence the resulting stalagmites, with low δ18O (∼-6‰ VSMOW) values indicative of strong convective activity, whilst high δ18O values (−4.5 and −5‰ VSMOW), are indicative of poor convection and proportionally more significant winter-frontal rainfall. We also demonstrate that the trace-element composition of drip water is largely modulated by PCP, and thus, the variability in underlying stalagmites can be interpreted to reflect changes in karst humidity, with low E/Ca ratios (E = Mg, Sr, Ba), indicative of a wet epikarst and high E/Ca ratios indicative of a dry epikarst. Our results provide essential information for the interpretation of the δ18O and trace element variability in stalagmites, which can result in robust paleoclimatic reconstructions from Gruta del Rey Marcos and elsewhere in central America and southern Mexico

A PARALLEL IMPLEMENTATION OF A SPECTRAL ELEMENT OCEAN MODEL FOR SIMULATING LOW-LATITUDE CIRCULATION SYSTEM

This paper is about the parallel implementation of a high-resolution, spectral element, primitive equation model of a homogeneous equatorial ocean. The present work shows that the high-order domain decomposition methods can be efficiently implemented in a massively parallel computing environment to solve large-scale CFD problems, such as the general circulation of the ocean

Decadal Arctic ice simulations: 1986-1995. Final report, September 1993--November 1997

The Arctic ice cover has been simulated for the period 1986-1995 with two coupled ice-ocean models, one with low resolution on a small polar stereographic plane (PIPS1/O), and one with high resolution on a rotated spherical grid (PIPS2), covering all northern hemispheric sea ice. The ice model used was the Hibler ice model, and the ocean models were both z-level types with rigid lid. Atmospheric forcing were derived from surface fluxes computed by the Navy`s NOGAPS global atmospheric prediction model

Massively Parallel Implementation of a High Order Domain Decomposition Equatorial Ocean Model

The present work is about the algorithms and parallel constructs of a spectral element equatorial ocean model. It shows that high order domain decomposition ocean models can be efficiently implemented on massively parallel architectures, such as the Connection Machine Model CM5. The optimized computational efficiency of the parallel spectral element ocean model comes not only from the exponential convergence of the numerical solution, but also from the work-intensive, medium-grained, geometry-based data parallelism. The data parallelism is created to efficiently implement the spectral element ocean model on the distributed-memory massively parallel computer, which minimizes communication among processing nodes. Computational complexity analysis is given for the parallel algorithm of the spectral element ocean model, and the model's parallel performance on the CM5 is evaluated. Lastly, results from a simulation of wind-driven circulation in low-latitude Atlantic ocean are described