OS13D-01 13:40h
Variability of Ocean Heat Content, Freshwater Content, and Steric Sea Level for the World Ocean- 1955-2002
We present estimates of the interdecadal variability of ocean heat content, freshwater content, and steric sea level for the world ocean during 1955-2002. We use the data in "World Ocean Database 2001" plus additional data recently acquired. Our new estimates are based on an additional 2 million historical and modern temperature profiles compared to earlier estimates.
OS13D-02 13:55h
Changes in the Density Field of the North Atlantic Over the Past Fifty Years
Analyses of oceanic temperature and salinity fields, via an examination of repeat cross-sections and historical hydrographic databases, have consistently revealed significant changes in the ocean's temperature and salinity fields over the past fifty years. While an understanding of these property changes is important for an assessment of the ocean's role as a heat and freshwater reservoir, it is the degree to which these changes are density compensated that sheds light on whether there are any dynamical consequences for the observed temperature and salinity changes. Our study focuses on an assessment of the temporal changes in the density field of the North Atlantic, a basin chosen for its unparalleled data density and its active thermohaline circulation. Specifically, we assess the spatial pattern of density changes over the past fifty years in this basin and quantify the contribution from temperature and salinity changes. A strong degree of compensation is found such that the density changes are smaller than what one would expect from an examination of the temperature or salinity fields in isolation. The cause of the compensation is discussed, as are the implications of the calculated density changes.
OS13D-03 14:10h
The All-Atlantic Temperature-Salinity-Pressure Relation and Regionally Variable Orthobaric Density
The availability of WOCE hydrographic data has prompted a careful reexamination of the relationship between temperature, salinity, and pressure in the Atlantic Ocean. Most of the observed thermodynamic properties are arranged onto three two-dimensional manifolds of three-dimensional thermodynamic space: a more saline northern branch and a fresher southern branch, each of which is nearly independent of pressure, and between them a bridge, on which density is nearly uniform at constant pressure. The properties of the branches are crucial to the construction of joint potential density surfaces, patched together at 1000 db intervals, as practiced by Reid. By resolving more finely in pressure (illustrated with 200 db spacing), a finer system of patched potential density surfaces can be obtained, and indeed the continuous limit can be taken to give a form of orthobaric density. Because it is based on the duplicate regional branches, this new form of orthobaric density is regionally differentiated. Using the properties of the bridge waters, a mapping can be devised to link the southern and northern forms of orthobaric density across the boundary between their respective regions of validity. Within the waters of the respective branches the regionally defined orthobaric isopycnals are very nearly material, limited only by inherent irreversible mixing processes. However, where these isopycnals cross the bridge waters, significant, reversible, material exchange across them may occur. In addition, a Montgomery function is defined within each region, but where the subdomains are patched together the Montgomery function is discontinuous. The idea of regional differentiation can also be extended to other ocean basins to create a variable useful for mapping observations or for use as the vertical coordinate in an isopycnal model on a global scale.
OS13D-04 14:25h
Location of the Polar Front from AMSR-E Satellite Sea Surface Temperature Measurements
The location of the polar front (PF) is mapped from the first two years of AMSR-E sea surface temperature (SST) measurements. The criteria used to determine the surface PF are first verified using {\it in situ} SST observations from high-resolution expendable bathythermograph (XBT) temperature measurements and by comparing to the subsurface PF location also determined from the XBT measurements. Consistent with previous studies, the mean path of the PF and its standard deviation are strongly influenced by bottom topography. However, the PF mean path diverges slightly from previous studies in several regions where there is high mesoscale variability. Both the PF location and SST at the PF show seasonal variations, with the southernmost location and the highest temperature during summer. The surface temperature of the PF varies along its path. SST at the PF is high in the Atlantic and Indian sections and is low in the Pacific section.
OS13D-05 14:40h
Subantarctic Mode Water and Antarctic Intermediate Water in the South Indian Ocean based on profiling floats 2000-2004
Four years of Argo float data between 2000 and 2004 have been used to study the properties of Subantarctic Mode Water (SAMW) and Antarctic Intermediate Water (AAIW) in relation to local winter mixed layer properties and frontal regimes in the South Indian Ocean. The accuracy of salinity in the selected Argo data set between $15^{\circ}$S and $40^{\circ}$S has been estimated to be better than 0.01 pss. The basin-wide synoptic view afforded by the float array showed that South Indian Ocean SAMW was more coherent, both in geographical and density space, than previously observed. Its density and thickness distributions are related to the winter mixed layer properties in the local Subantarctic Zone, with progressively denser and thicker SAMW observed to the east. The increase in SAMW thickness east of $70^{\circ}$E may be due to the widening of the Subantarctic Zone after passing the Kerguelen Plateau. South Indian Ocean AAIW was centred on $\sigma_{\theta} = 27.2$ kg m$^{-3}$, with $\theta$-S properties comparable to those of the winter mixed layer in the local Polar Frontal Zone. As observed by previous hydrographic surveys, low-salinity AAIW was injected northward into the subtropical gyre in mid-basin, about $65^{\circ}$E to $80^{\circ}$E. Argo profiles showed that this northward flow extended to the northern extent of the study region at $15^{\circ}$S. The latitude band $30^{\circ}$S to $40^{\circ}$S has the least meridional salinity gradient on density surfaces in AAIW, so it is the best place to detect any consolidated decadal changes in the salinity minimum of South Indian Ocean AAIW.
OS13D-06 14:55h
Eddy Heat Fluxes in the Subtropical North Pacific from Argo, TMI and Altimetry Measurements
Basin-scale heat transport induced by mesoscale oceanic eddies is estimated by combining satellite-derived sea surface height and temperature data with Argo float temperature/salinity data. In the North Pacific subtropical gyre, warm (cold) temperature anomalies of mesoscale eddies are found to be consistently located to the west of high (low) SSH anomalies. The phase misalignment between the temperature and velocity anomalies, however, is largely confined to the seasonal thermocline, causing most of the eddy-induced heat transport to be carried in the surface 200\,m layer. By establishing a statistical relationship between the surface and depth-integrated values of the eddy heat transport, the basin-scale eddy heat transport is derived from the concurrent satellite SSH/SST data of the past 6 yrs. In the Kuroshio Extension region, the meandering zonal jet is found to generate oppositely signed eddy heat fluxes. As a result, the zonally integrated poleward heat transport associated with the Kuroshio Extension is at a level of $O(0.1$\,pW), smaller than the previous estimates based on turbulent closure schemes. Large poleward eddy heat transport is also found in the subtropical North Pacific along a SW-NE tilting band between Taiwan and the Midway Islands. This band corresponds to the region of the Subtropical Front and it is argued that the relevant temperature field for identifying this band in the turbulent closure scheme models should be that averaged over the seasonal thermocline.
http://www.soest.hawaii.edu/oceanography/bo/QC05_inpress.pdf
OS13D-07 15:10h
Meanders Downstream the Agulhas Retroflexion.
The Agulhas Current is a jet in the Eastern Indian Ocean that suffers a dramatic anticyclonic turn once it advances over the southernmost latitude of the African continent. From flowing poleward and parallel to the coast in a southwestward direction turns into an eastward direction, followed by large meanders. The global drifter program allows an estimation of these features in the mean surface flow and the variability. We do an analysis of five meanders, their wavelength is about 700 km, and their amplitude decrease from 170 km in the first one to 50 km in the following. Theories of the main expected dynamical balance in steady or quasi-steady geophysical jets had been around for 40 years. Conservation of potential vorticity, and therefore neglect of dissipative processes, being at the core of these theories. Here we show that the large meanders follow a simple vorticity balance, in agreement with such theories, where the planetary vorticity and curvature of the flow add up to a constant along pathlines. We argue on the low influence of the Reynolds stresses given the ratio of eddy and mean kinetic energy.
OS13D-08 15:25h
Caribbean Current and Eddies as Observed by Surface Drifters
Recent satellite-tracked surface drifter trajectories were analyzed to describe the mean currents and eddies in the Caribbean Sea. The structure of the Caribbean Current and its variability were determined from high-resolution degree maps of the mean velocity and eddy kinetic energy. Looping drifter trajectories were used to identify discrete cyclones and anticyclones, and their characteristics were described and related to the structure of the mean flow. The translation rate of eddies in different areas was found to be similar to the mean velocity of the local background flow fields suggesting that the eddies were largely advected by the background flow. Ten energetic anticyclones translated westward at 13 cm/sec in the Venezuela and Colombia Basins. These anticyclones tended to lie in two bands, centered near 15°N and 17°N, coinciding with two jets of the Caribbean Current. The northern weaker jet contains water primarily from the North Atlantic, the southern stronger jet contains water from the tropical and South Atlantic. The anticyclones are thought to have formed in the eastern Caribbean from the anticyclonic vorticity derived from North Brazil Current rings. The ring vorticity enters the eastern Caribbean through island passages and is probably amplified by the anticyclonic shear on the northern side of the jets. Southwest of Cuba a cyclone-anticyclone pair was observed to slowly (~ 2 cm/sec) translate westward into the Yucatan Current. The cyclone was tracked for 10.5 months with four drifters, making it the longest-tracked of the Caribbean eddies.