Pacific Ocean water balance

Gagan M. K., Ayliffe L. K., Hopley D., Cali J. A., Mortimer G. E., Chappell J., McCulloch M. T., and Head M. J. (1998) Temperature and surface-ocean water balance of the Mid-Holocene tropical western pacific. Science 279, 1014-1018. 

Kharkar DP, Thomson J, Turekian KK, Forster WO (1976) Uranium and thorium series nuclides in plankton from the Caribbean. Limnol Oceanogr 21 294-299 Krishnaswami S, Lai D, Somayajulu BLK, Weiss R, Craig H (1976) Large-volume in situ filtration of deep Pacific waters mineralogical and radioisotope studies. Earth Planet Sci Lett 32 420-429 Livingston HD, Cochran JK (1987) Determination of transuranic and thorium isotopes in ocean water in solution and in filterable particles. J Radioanal Nucl Chem 115 299-308 Masque P, Sanchez-Cabeza JA, Braach JM, Palacios E, Canals M (2002) Balance and residence times of °Pb and 4 o in surface waters of the northwestern Mediterranean Sea. Cont Shelf Res 22 2127-2146 Matsumoto E (1975) Th-234-U-238 radioactive disequilibrium in the surface layer of the oceans. Geochim Cosmochim Acta 39 205-212... 

Water exchange through the southern boundary of the Norwegian Sea is V3. The water temperature T k in Eijk (block MWT) is a function of evaporation, precipitation, river flows, and inflows of water from the Atlantic and Pacific Oceans. Its change with time in Etjk is described by the equation of heat balance ... 

Betzer et al. (1984, 1986) studied the sedimentation of pteropods and foraminifera in the North Pacific. Their sediment trap results confirmed that considerable dissolution of pteropods was taking place in the water column. They calculated that approximately 90% of the aragonite flux was remineralized in the upper 2.2 km of the water column. Dissolution was estimated to be almost enough to balance the alkalinity budget for the intermediate water maximum of the Pacific Ocean. It should be noted that the depth for total dissolution in the water column is considerably deeper than the aragonite compensation depth. This is probably due to the short residence time of pteropods in the water column because of their rapid rates of sinking. 

In the large perspective, the North Atlantic Ocean is now saltier than the North Pacific as a result of the present distribution of ocean and atmosphere currents and continents over the surface of the Earth. Other distributions, as occurred in the past owing to different distributions of ice, deserts or continental topography, would produce very different water balances and global current systems. 

Studies carried out to evaluate the uptake of Fe by phytoplankton showed that only the dissolved metal is bioavailable and that a thermal or photochemical treatment is necessary for the colloidal Fe to become bioavailable (163). Moreover, the chemical form in which Fe is present can also affect its availability for plankton. The distribution of Fe(II) in the euphotic layer of the equatorial Pacific Ocean was examined by O Sullivan et al. (164). Its concentration is regulated by the balance between production and removal Fe(II) can be produced by microbial and chemical reduction, while the loss in surface water is controlled by biological uptake and by oxidation to Fe(III), subsequent hydrolysis, ageing and settling. The results showed maximum concentration near the surface and at the depths with higher chlorophyll a levels, the concentration ranging between 0.12 and 0.53 nM. Laboratory experiments carried out by the same authors showed that photoreduction can be an important source of Fe(II). Considering the different chemical speciation observed at various depths, different bioavailability can be expected in the examined zone. 

O.C. Zafiriou, S.A. Andrews, W. Wang. Concordant estimates of oceanic carbon monoxide source and sink processes in the Pacific yield a balanced global blue-water CO budget, Global Biogeochem. Cycles, in press. 

Thermodynamic calculations show that chromate is the expected form in oxygenated sea water, while the insoluble Cr(III) species would predominate in very low-oxygen (so called suboxic ) or anoxic waters. However, it is important to note that thermodynamic calculations only predict elemental spe-ciation at equilibrium (when the rates of formation and destruction are balanced), but they do not consider the rates of conversion themselves. For example, Cr(III) should not exist in oxygenated sea water, but its rate of oxidation to Cr(VI) is slow (days to months), meaning that Cr(III) can persist in oxic water ( kinetic stabilization ). In the eastern North Pacific Ocean, Cr(VI) displays a surface concentration of 3 nmol 1 (Figure 2A), but then decreases rapidly to a minimum of 1.7 nmol 1 at 300 m depth and increases below this to levels of 4-5 nmol in the deeper waters. While chromate appears to display a mixture of scavenged and nutrient-like behavior, the Cr(VI) minimum occurs at the same depth as the widespread suboxic zone in the eastern Pacific. 

Dimethyl sulfide (DMS), through its oxidation to sulfate in the troposphere, acts as a source of cloud condensation nuclei, thus potentially influencing the radiative balance of the atmosphere. DMS is formed in sea water through the microbial decomposition of dimethyl sulfonioproprionate (DMSP), a compound believed to act as an osmolyte in certain species of marine phytoplankton. The flux of DMS to the atmosphere is controlled by its concentration in surface sea waters, which is controlled in turn by the rate of its decomposition. Estimates indicate that 7-40% of the total turnover of DMS in the surface waters of the Pacific Ocean is due to the photosensitized destruction of this compound, illustrating the potential importance of this pathway in controlling the flux of DMS to the atmosphere. 

Scavenged type Trace metals such as Al, Co, Ce, and Bi, show surface enrichment and depletion in deep waters, in contrast to the opposite trend in nutrient types. These elements are highly particle-reactive and are rapidly removed from the water column by sinking particulate matter and/or by scavenging at the sediment-water interface. Their mean oceanic residence times are short (<10 -10 years). Interoceanic variations in their concentration can be large (e.g., Atlantic/Pacific concentration ratio 40 for Al) depending on kinetic balance between supply and removal for the specific basins. 

Observations from studies of surface sediments have allowed definition of regionally varying levels in the ocean at which pronounced changes in the presence or preservation of calcium carbonate result from the depth-dependent increase of dissolution on the seafloor. The first such level to be identified was simply the depth boundary in the ocean separating carbonate-rich sediments above from carbonate-free sediments below. This level is termed the calcite (or carbonate) compensation depth (CCD) and represents the depth at which the rate of carbonate dissolution on the seafloor exactly balances the rate of carbonate supply from the overlying surface waters. Because the supply and dissolution rates of carbonate differ from place to place in the ocean, the depth of the CCD is variable. In the Pacific, the CCD is typically found at depths between about 3500 and 4500 m. In the North Atlantic and parts of the South Atlantic, it is found... 

One of the first applications of ocean radiocarbon data was as a constraint on the vertical diffusivity, upwelling, and oxygen consumption rates in the deep waters below the main thermocline. As illustrated in Figure 2, the oxygen and radiocarbon concentrations in the North Pacific show a minimum at mid-depth and then increase toward the ocean seabed. This reflects particle remineralization in the water column and the inflow and gradual upwelling of more recently ventilated bottom waters from the Southern Ocean. Mathematically, the vertical profiles for radiocarbon, oxygen (O2), and a conservative tracer salinity (5) can be posed as steady-state, 1-D balances ... 

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