Lynne D. Talley

Distribution and Formation of North Pacific Intermediate Water

Abstract The North Pacific Intermediate Water (NPIW), defined as the main salinity minimum in the subtropical North Pacific, is examined with respect to its overall property distributions. These suggest that NPIW is formed only in the northwestern subtropical gyre; that is, in the mixed water region between the Kuroshio Extension and Oyashio front. Subsequent modification along its advective path increases its salinity and reduces its oxygen. The mixed water region is studied using all bottle data available from the National Oceanographic Data Center, with particular emphasis on several winters. Waters from the Oyashio, Kuroshio, and the Tsugaru Warm Current influence the mixed water region, with a well-defined local surface water mass formed as a mixture of the surface waters from these three sources. Significant salinity minima in the mixed water region are grouped into those that are directly related to the winter surface density and are found at the base of the oxygen-saturated surface layer, and thos...

Distribution and Circulation of Labrador Sea Water

Abstract Labrador Sea Water is the final product of the cyclonic circulation of Subpolar Mode Water in the open northern North Atlantic (McCartney and Talley, 1982). The temperature and salinity of the convectively formed Subpolar Mode Water decrease from 14.7°C, 36.08‰ to 3.4°C, 34.88‰ on account of the cumulative effects of excess precipitation and cooling. The coldest Mode Water is Labrador Sea Water, which spreads at mid-depths and is found throughout the North Atlantic Ocean north of 40°N and along its western boundary to 18°N. A vertical minimum in potential vorticity is used as the primary tracer for Labrador Sea Water. Labrador Sea Water is advected in three main directions out of the Labrador Sea: 1) northeastward into the Irminger Sea, 2) southeastward across the Atlantic beneath the North Atlantic current, and 3) southward past Newfoundland with the Labrador Current and thence westward into the Slope Water region, crossing under the Gulf Stream off Cape Hatteras. The Labrador Sea Water core is ...

The Subpolar Mode Water of the North Atlantic Ocean

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Data-Based Meridional Overturning Streamfunctions for the Global Ocean

Abstract The meridional overturning circulation for the Atlantic, Pacific, and Indian Oceans is computed from absolute geostrophic velocity estimates based on hydrographic data and from climatological Ekman transports. The Atlantic overturn includes the expected North Atlantic Deep Water formation (including Labrador Sea Water and Nordic Sea Overflow Water), with an amplitude of about 18 Sv through most of the Atlantic and an error of the order of 3–5 Sv (1 Sv ≡ 106 m3 s−1). The Lower Circumpolar Deep Water (Antarctic Bottom Water) flows north with about 8 Sv of upwelling and a southward return in the South Atlantic, and 6 Sv extending to and upwelling in the North Atlantic. The northward flow of 8 Sv in the upper layer in the Atlantic (sea surface through the Antarctic Intermediate Water) is transformed to lower density in the Tropics before losing buoyancy in the Gulf Stream and North Atlantic Current. The Pacific overturning streamfunction includes 10 Sv of Lower Circumpolar Deep Water flowing north in...

Shallow, Intermediate, and Deep Overturning Components of the Global Heat Budget

Abstract The oceans overturning circulation and associated heat transport are divided into contributions based on water mass ventilation from 1) shallow overturning within the wind-driven subtropical gyres to the base of the thermocline, 2) overturning into the intermediate depth layer (500–2000 m) in the North Atlantic and North Pacific, and 3) overturning into the deep layers in the North Atlantic (Nordic Seas overflows) and around Antarctica. The contribution to South Pacific and Indian heat transport from the Indonesian Throughflow is separated from that of the subtropical gyres and is small. A shallow overturning heat transport of 0.6 PW dominates the 0.8-PW total heat transport at 24°N in the North Pacific but carries only 0.1–0.4 PW of the 1.3-PW total in the North Atlantic at 24°N. Shallow overturning heat transports in the Southern Hemisphere are also poleward: −0.2 to −0.3 PW southward across 30°S in each of the Pacific and Indian Oceans but only −0.1 PW in the South Atlantic. Intermediate wate...

Potential Vorticity Distribution in the North Pacific

Abstract Vertical sections and maps of potential vorticity ρ−1f∂ρ/∂z for the North Pacific are presented. On shallow isopycnals, high potential vorticity is found in the tropics, subpolar gyre, and along the eastern boundary of the subtropical gyre, all associated with Ekman upwelling. Low potential vorticity is found in the western subtropical gyre (subtropical mode water), in a separate patch near the sea surface in the eastern subtropical gyre and extending around the gyre, and near sea-surface outcrops in the subpolar gyre; the last is analogous to the subpolar mode water of the North Atlantic and Southern Ocean. Meridional gradients of potential vorticity are high between the subtropical and subpolar gyres at densities which outcrop only in the subpolar gyre; lateral gradients of potential vorticity are low in large regions of the subtropical gyre on these isopycnals. On slightly denser isopycnals which do not outcrop in the North Pacific, there are large regions of low potential vorticity gradients ...

North Pacific Intermediate Water in the Kuroshio/Oyashio Mixed Water Region

Abstract The North Pacific Intermediate Water (NPIW) originates as a vertical salinity minimum in the mixed water region (MWR) between the Kuroshio and Oyashio, just east of Japan. Salinity minima in this region are examined and related to the water man structures, dynamical features, and winter mixed layer density of waters of Oyashio origin. Stations in the MWR are divided into five regimes, of which three represent source waters (from the Kuroshio, Oyashio, and Tsugaru Current) and two are mixed waters formed from these three inputs. Examination of NPIW at stations just east of the MWR indicates that the mixed waters in the MWR are the origin of the newest NPIW. Multiple salinity minima with much finestructure are seen throughout the MWR in spring 1989, with the most fragmented occurring around the large warm core ring centered at 37°N, 144°E, suggesting that this is a dominant site for salinity minimum formation. The density of the NPIW in the MWR is slightly higher than the apparent late winter surfa...

Warm-to-Cold Water Conversion in the Northern North Atlantic Ocean

Abstract A box Model of warm-to-cold-water conversion in the northern North Atlantic is developed and used to estimate conversion rates, given water mass temperatures, conversion paths and rate of air-sea heat exchange. The northern North Atlantic is modeled by three boxes, each required to satisfy heat and mass balance statements. The boxes represent the Norwegian Sea, and a two-layer representation of the open subpolar North Atlantic. In the Norwegian Sea box, warm water enters from the south, is cooled in the cyclonic gyre of the Norwegian–Greenland Sea, and the colder water returns southwards to the open subpolar North Atlantic. Some exchange with the North Polar Sea also is included. The open subpolar North Atlantic has two boxes. In the abyssal box, the dense overflows from the Norwegian Sea flow south, entraining warm water from the upper-ocean box. In the upper-ocean box, warm water enters from the south, supplying the warm water for an upper ocean cyclonic circulation that culminates in productio...

Antarctic Intermediate Water in the South Atlantic

Maps of the Antarctic Intermediate Water (AAIW) in the Atlantic, and on a global isopycnal which intersects the AAIW in the south, show the location and properties of the salinity and oxygen extrema associated with the AAIW, and the likely sources of AAIW. These are primarily the surface waters in the southeastern Pacific, which produce the South Pacific AAIW, and surface waters in northern Drake Passage and the Falkland Current loop, which produce the South Atlantic AAIW. This latter source is the primary one for AAIW of the Indian Ocean as well. Winter surface properties and annual-averaged Ekman pumping and S verdrup transport for the southern hemisphere suggest that the formation density of the AAIW is the highest density which can be subducted in the South Pacific. The higher density of AAIW in the South Atlantic may result from more complex processes. The connection between the subtropical gyres of the Atlantic and Indian and between the Indian and Pacific Oceans contributes to modification of AAIW as it spreads tortuously northward around the subtropical gyres. Potential vorticity and AAIW salinity and oxygen illustrate the near barrier between the subtropical and tropical regimes, at about 20°to 25°north and south of the equator. Communication between the regimes is primarily through the western boundary currents.

An eastern Atlantic section from Iceland southward across the equator

A long CTD/hydrographic section with closely-spaced stations was occupied In July- August 1988 from Iceland southward to 3°S along a nominal longitude of 20°W The section extends from the surface down to the bottom, and spans the entire mid-ocean circulation regime of the North Atlantic from the subpolar gyre through the subtropical gyre and the equatorial currents Vertical sections of potential temperature, sahnlty and potential density from CTD measurements and of oxygen, silica, phosphate and nitrate, based on d~screte water-sample measurements are presented and discussed in the context of the large-scale circulation of the North Atlantic Ocean The close spacing of hlgh-quahty stations reveals some leatures not described previously The more important findings include ( 1 ) possible reclrculation of the hghtest Subpolar Mode Water into the tropics, (2) a thermostad at temperatures of 8-9°C, lying below that of the Equatorial 13°C Water, (3) the nutrient distribution in the low-sallmty water above the Mediterranean Outflow Water that supports the previous conjecture of northern influence ot the Antarctic Intermedmte Water. 14) a great deal of lateral structure of the Mediterranean Outflow Water, with a number of lobes of high sahnlt), (5) an abrupt southern boundary ot the Labrador Sea Water at the Azores-Biscay Rise and a vertically well-mixed region to its south, (6) a sharp demarcation in the central Iceland Basra between the newest Iceland-Scotland Overflow Water and older bottom water, which has a significant component of southern water, (7) evidence that the Northeast Atlantic Deep Water is a mixture ot the Mediterranean Outflow Water and the Northwest Atlantic Bottom Water with very httle input from the Iceland-Scotland Overflow Water, (8) an usolated core of the high-salinity, low-silica Upper North Atlantic Deep Water at the equator, (9) a core of the high-oxygen, low- nutrient Lower North Atlannc Deep Water pressed against the southern flank of the Mld-Atlanuc Ridge just south of the equator, (10) a weak minimum of salinity, and well-defined maxima of nutrients associated with the oxygen minimum that separates the Middle and Lower North Atlantic Deep Waters south ot the equator, (11) a large body ol nearly homogeneous water beneath the Middle North Atlantic Deep Water between 2(1°N and the Azores-Biscay Rise, and (i 2) a deep westward boundary undercurrent on the southern slope of the Rockall Plateau