Arnold L. Gordon

Bio: Arnold L. Gordon is an academic researcher from Lamont–Doherty Earth Observatory. The author has contributed to research in topics: Thermocline & Thermohaline circulation. The author has an hindex of 75, co-authored 272 publications receiving 18243 citations. Previous affiliations of Arnold L. Gordon include University of Miami & Columbia University.

Interocean Exchange of Thermocline Water

Abstract: Formation of North Atlantic Deep Water (NADW) represents a transfer of upper layer water to abyssal depths at a rate of 15 to 20 x 10 6 m3/s. NADW spreads throughout the Atlantic Ocean and is exported to the Indian and Pacific Oceans by the Antarctic Circumpolar Current and deep western boundary currents. Naturally, there must be a compensating flow of upper layer water toward the northern North Atlantic to feed NADW production. It is proposed that this return flow is accomplished primarily within the ocean's warm water thermocline layer. In this way the main thermoclines of the ocean are linked as they participate in a thermohaline-driven global scale circulation cell associated with NADW formation. The path of the return flow of warm water is as follows: Pacific to Indian flow within the Indonesian Seas, advection across the Indian Ocean in the 10o-15oS latitude belt, southward transfer in the Mozambique Channel, entry into the South Atlantic by a branch of the Agulhas Current that does not complete the retroflection pattern, northward advection within the subtropical gyre of the South Atlantic (which on balance with the southward flux of colder North Atlantic Deep Water supports the northward oceanic heat flux characteristic of the South Atlantic), and cross-equatorial flow into the western North Atlantic. The magnitude of the return flow increases along its path as more NADW is incorporated into the upper layer of the ocean. Additionally, the water mass characteristics of the return flow are gradually altered by regional ocean-atmosphere interaction and mixing processes. Within the Indonesian seas there is evidence of strong vertical mixing across the thermocline. The cold water route, Pacific to Atlantic transport of Subantarctic water within the Drake Passage, is of secondary importance, amounting to perhaps 25% of the warm water route transport. The continuity or vigor of the warm water route is vulnerable to change not only as the thermohaline forcing in the northern North Atlantic varies but also as the larger-scale wind-driven criculation factors vary. The interocean links within the Indonesian seas and at the Agulhas retroflection may be particularly responsive to such variability. Changes in the warn: water route continuity may in turn influence formation characteristics of NADW.

Southern Ocean fronts from the Greenwich Meridian to Tasmania

Abstract: All available meridional sections have been analyzed to investigate the evolution of main fronts between 0° and 150°E. The central South Atlantic is featured by the Subtropical Frontal Zone (STFZ), bordered by the North and South Subtropical Fronts (NSTF and SSTF, respectively), and by the Polar Frontal Zone (PFZ), bordered by the Subantarctic and Polar Fronts (SAF and PF, respectively). This structure becomes more complex in the African sector as the Agulhas Retroflection and the bottom topography force a more convoluted pattern. The Retroflection and associated Agulhas Front (AF) press the SSTF from 38° to 42°–43°S. Strong interactions of the AF, SSTF, and SAF with topography shift the fronts but do not obliterate them. The AF can be traced reliably up to 52°E, sometimes up to 75°E. The SAF is deflected from 45° to 43°S by the Mid-Ocean Ridge and converges with the SSTF north of the Prince Edward Islands to form a combined SSTF/SAF. This front intensifies east of 50°–52°E as a result of the confluence with the AF, and between 52° and 65°E a triple AF/SSTF/SAF (“the Crozet Front”) is observed. The PF continues along 49° and 50°S between the Crozet Plateau and the Ob-Lena (Conrad) Rise, passing north of Kerguelen, nearly joining the triple Crozet Front. Downstream of the Kerguelen-Amsterdam Passage, the canonical structure is being restored (SSTF, SAF, PF); however, the front parameters in the Australian sector are different from the African sector, largely because of strong air-sea interaction and cross-frontal exchanges in the Crozet-Kerguelen region. The SSTF, squeezed between the AF and SAF, loses characteristics to both. The SSTF/SAF interaction results in the Australian SAF being warmer and saltier downstream, while the SSTF becomes shallower and weaker. The Australian STF derives its characteristics mostly from the AF, thus bringing the modified Agulhas waters to the Pacific Ocean. The newly defined North Subtropical Front (NSTF) was distinguished in the Indian Ocean between 31° and 38°S. The front marks the southern boundary of the subtropical salty, warm water pool of the central South Indian Ocean. The NSTF location is coincident with the position of the wind convergence between westerlies and easterlies, suggesting the possible wind-driven frontogenesis.

Pathways of water between the Pacific and Indian oceans in the Indonesian seas

Abstract: THE physical structure of the Pacific and Indian oceans is substantially affected by the inter-ocean transport of excess fresh water from the North Pacific Ocean through the Indonesian seas1,2. The efficiency of this transport is an important regulator of the meridional overturning of these oceans1,2, and hence perhaps of the global thermohaline circulation3; in addition, the seepage of warm water out of the Pacific affects the volume of the western Pacific warm pool, and thus may influence EI Nino events24. But the sources, pathways and physical properties of the Indonesian throughflow are not well enough characterized to allow its influence on ocean circulation and the climate system to be quantified. Here we report salinity, temperature and chemical-tracer data from the Indonesian seas which show that the throughflow is dominated by two components: one of low-salinity, well ventilated North Pacific water through the upper thermocline of the Makassar Strait, and the other of more saline South Pacific water through the lower thermocline of the eastern Indonesian seas. Seasonal (monosonal) variations in the ratio of these components, perhaps modulated by EI Nino conditions, imply the existence of potentially important variable feedbacks to the ocean circulation and climate system.

Pacific western boundary currents and their roles in climate

Abstract: Pacific Ocean western boundary currents and the interlinked equatorial Pacific circulation system were among the first currents of these types to be explored by pioneering oceanographers. The widely accepted but poorly quantified importance of these currents-in processes such as the El Nino/Southern Oscillation, the Pacific Decadal Oscillation and the Indonesian Throughflow-has triggered renewed interest. Ongoing efforts are seeking to understand the heat and mass balances of the equatorial Pacific, and possible changes associated with greenhouse-gas-induced climate change. Only a concerted international effort will close the observational, theoretical and technical gaps currently limiting a robust answer to these elusive questions.

Prokaryotes: The unseen majority

Abstract: The number of prokaryotes and the total amount of their cellular carbon on earth are estimated to be 4-6 3 10 30 cells and 350-550 Pg of C (1 Pg 5 10 15 g), respectively. Thus, the total amount of prokaryotic carbon is 60-100% of the estimated total carbon in plants, and inclusion of prokaryotic carbon in global models will almost double estimates of the amount of carbon stored in living organisms. In addition, the earth's prokaryotes contain 85-130 Pg of N and 9-14 Pg of P, or about 10-fold more of these nutrients than do plants, and represent the largest pool of these nutrients in living organisms. Most of the earth's prokaryotes occur in the open ocean, in soil, and in oceanic and terrestrial subsurfaces, where the numbers of cells are 1.2 3 10 29 , 2.6 3 10 29 , 3.5 3 10 30 , and 0.25-2.5 3 10 30 , respectively. The numbers of het- erotrophic prokaryotes in the upper 200 m of the open ocean, the ocean below 200 m, and soil are consistent with average turnover times of 6-25 days, 0.8 yr, and 2.5 yr, respectively. Although subject to a great deal of uncertainty, the estimate for the average turnover time of prokaryotes in the subsurface is on the order of 1-2 3 10 3 yr. The cellular production rate for all prokaryotes on earth is estimated at 1.7 3 10 30 cellsyyr and is highest in the open ocean. The large population size and rapid growth of prokaryotes provides an enormous capacity for genetic diversity. Although invisible to the naked eye, prokaryotes are an essential component of the earth's biota. They catalyze unique and indispensable transformations in the biogeochemical cy- cles of the biosphere, produce important components of the earth's atmosphere, and represent a large portion of life's genetic diversity. Although the abundance of prokaryotes has been estimated indirectly (1, 2), the actual number of pro- karyotes and the total amount of their cellular carbon on earth have never been directly assessed. Presumably, prokaryotes' very ubiquity has discouraged investigators, because an esti- mation of the number of prokaryotes would seem to require endless cataloging of numerous habitats. To estimate the number and total carbon of prokaryotes on earth, several representative habitats were first examined. This analysis indicated that most of the prokaryotes reside in three large habitats: seawater, soil, and the sedimentysoil subsur- face. Although many other habitats contain dense populations, their numerical contribution to the total number of pro- karyotes is small. Thus, evaluating the total number and total carbon of prokaryotes on earth becomes a solvable problem. Aquatic Environments. Numerous estimates of cell density, volume, and carbon indicate that prokaryotes are ubiquitous in marine and fresh water (e.g., 3-5). Although a large range of cellular densities has been reported (10 4 -10 7 cellsyml), the

Climate Change 2007: The Physical Science Basis.

Abstract: Cause, conseguenze e strategie di mitigazione Proponiamo il primo di una serie di articoli in cui affronteremo l’attuale problema dei mutamenti climatici. Presentiamo il documento redatto, votato e pubblicato dall’Ipcc - Comitato intergovernativo sui cambiamenti climatici - che illustra la sintesi delle ricerche svolte su questo tema rilevante.

Monsoons: Processes, predictability, and the prospects for prediction

Abstract: The Tropical Ocean-Global Atmosphere (TOGA) program sought to determine the predictability of the coupled ocean-atmosphere system. The World Climate Research Programme's (WCRP) Global Ocean-Atmosphere-Land System (GOALS) program seeks to explore predictability of the global climate system through investigation of the major planetary heat sources and sinks, and interactions between them. The Asian-Australian monsoon system, which undergoes aperiodic and high amplitude variations on intraseasonal, annual, biennial and interannual timescales is a major focus of GOALS. Empirical seasonal forecasts of the monsoon have been made with moderate success for over 100 years. More recent modeling efforts have not been successful. Even simulation of the mean structure of the Asian monsoon has proven elusive and the observed ENSO-monsoon relationships has been difficult to replicate. Divergence in simulation skill occurs between integrations by different models or between members of ensembles of the same model. This degree of spread is surprising given the relative success of empirical forecast techniques. Two possible explanations are presented: difficulty in modeling the monsoon regions and nonlinear error growth due to regional hydrodynamical instabilities. It is argued that the reconciliation of these explanations is imperative for prediction of the monsoon to be improved. To this end, a thorough description of observed monsoon variability and the physical processes that are thought to be important is presented. Prospects of improving prediction and some strategies that may help achieve improvement are discussed.

On the meridional extent and fronts of the Antarctic Circumpolar Current

Abstract: Large-scale features of the Antarctic Circumpolar Current (ACC) are described using all historical hydrographic data available from the Southern Ocean. The geopotential anomaly of the sea surface relative to 1000 db reveals the highly-sheared eastward flow of the ACC and the strong steering of the current by the ridge system around Antarctica. The near-surface property distributions differentiate the ACC waters from the warmer and saltier waters of the subtropical regimes. The Subtropical Front (STF), interrupted only by South America, marks the northern most extent of subantarctic waters. Distributions of properties on isopycnal surfaces show an abrupt end to the characteristic signal of the Upper Circumpolar Deep Water (UCDW), as this water mass shoals southward and is entrained into the surface mixed layer. This sharp water mass boundary nearly coincides with the southernmost circumpolar streamline passing through Drake Passage. To its south are the weakly-sheared circulations of the subpolar regime. Inspection of many hydrographic crossings of this transition reveals that the poleward edge of the UCD W signal is a reasonable definition of the southern boundary of the ACC. At Drake Passage, three deep-reaching fronts account for most of the ACC transport. Well-established indicators of the Subantarctic Front and Polar Front are traced unbroken around Antarctica. The third deep-reaching front observed to the south of the Polar Front at Drake Passage also continues with similar characteristics as a circumpolar feature. It is called here the southern ACC front. Stations from multiple synoptic transects of these circumpolar fronts are used to describe the average property structure within each ACC zone. Between the STF and the southern boundary of the ACC, the shear transport of the circumpolar current above 3000 m is at all longitudes about 100 Sv (1 Sv = 106 m3 s−) eastward.