Central Ocean Region Research Articles

Climatology of Anticyclonic and Cyclonic Rossby Wave Breaking on the Dynamical Tropopause in the Southern Hemisphere

Abstract The characteristics of the climatological distribution of the anticyclonic (LC1) and cyclonic (LC2) Rossby wave breaking (RWB) in the Southern Hemisphere (SH) are investigated by calculating the occurrence frequency of the LC1- and LC2-like stratospheric potential vorticity (PV) streamers in the SH during the austral summer [December–February (DJF)] and wintertime [June–August (JJA)] on several isentropic surfaces by using the 40-yr European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA-40) daily dataset. The results show that 1) on the equatorward flank of the climatological midlatitude jet (MLJ), the LC1-like PV streamers are frequently found over the central oceanic regions, whereas the LC2-like PV streamers are almost absent. On the poleward flank of the climatological MLJ, both types of PV streamers are frequently observed and the LC2-like PV streamers predominate; 2) the regions where the occurrences of the PV streamers are frequent overlap the weak zonal wind regions; and 3) in austral winter, a “double-jet” setting is evident in two regions of the SH [the double-jet upstream (DU) and the spilt jet region]. In the double-jet setting regions, the LC1-like PV streamers are frequently found both in the DU and the split-jet regions, while the occurrence of the LC2-like PV streamers is frequent in the split-jet region but is rather infrequent in the DU region.

Large, deep-sea agglutinated Foraminifera; two differing kinds of organization and their possible ecological significance

We consider two groups of deep-sea agglutinated foraminifera: 1) robust, tubular astrorhizaceans (Bathysiphon, Rhabdammina) and hippocrepinaceans (Hyperammina, Saccorhiza) which reach several centimeters or more in length and contain a substantial protoplasmic mass (sarcode); and 2) delicate komokiaceans with tests typically 1-5 mm in size and forming a branching tubule system containing accumulations of stercomata and sparse protoplasm, sometimes with fine sediment incorporated between the tubules to form a mudball structure. The tubular taxa occur in eutrophic settings, usually on continental margins, where the food supply originates from strong surface primary production, currents, or downslope transport. We speculate that they are opportunists, able to grow fairly quickly when food is available. The sarcode may provide a buffer against periods of food shortage, enabling these taxa to take advantage of a relatively high but fluctuating food input. Komokiaceans, on the other hand, have a large volume/low biomass organization and are most important in oligotrophic, central oceanic regions. We speculate that the combination of relatively body size and low protoplasmic content may reflect slow growth and longevity; it may also serve to reduce the food content of komokiaceans and hence their attractiveness to predators. In order to illustrate these contrasting groups, we briefly consider faunas from the Oman margin (3400 m depth) and NE Atlantic abyssal plains (4850-4950 m depth), distinguishing between: 1) oligotrophic, central oceanic regions rich in komokiaceans (Madeira Abyssal Plain); 2) central oceanic regions with seasonal phytodetritus inputs where komokiaceans coexist with small (

Some recent advances in the study of deep-sea foraminiferal biology and their palaeoecological significance

During the past two decades, biologists have become increasingly aware of the diversity and abundance of foraminifera in marine benthic ecosystems. These protists are probably the most important eukaryotes present in ocean floor communities. In some areas, particularly central oceanic regions, foraminiferal assemblages are dominated by newly discovered, soft-bodied forms with morphologies quite unlike those of “conventional” foraminifers and with little fossilisation potential. However, despite the presumed loss of these delicate forms from the fossil record, foraminiferal tests are still the only microfossils to occur commonly in ancient deep-sea sediments. Thus, they are a focus of attention for both geologists and biologists. This presentation will concentrate on two main areas of biological research which have palaeontological significance.Foraminiferal microhabitats. Recent research indicates that particular species tend to live infaunally (deep or shallow), epifaunally or suprabenthically. Growth above or below the sediment-water interface has major implications for the stable isotope chemistry of calcareous tests, an important tool in palaeooceanography. Other species inhabit organic detritus composed of phytoplankton material rapidly sedimented from the euphotic zone. This “phytodetritus” arrives suddenly on the ocean floor following the spring bloom and is quickly colonized by foraminiferal species which feed on it, reproduce and rapidly develop large populations. These populations collapse when the food source is exhausted. The direct consumption of phytodetritus (and other organic matter inputs) by benthic foraminifers may be a widespread phenomenon which influences their population dynamics, regional distribution patterns and isotope chemistry.Recolonization. The defaunation of large tracts of ocean floor by turbidity currents or anoxic events must have happened on countless occasions over geological time, particularly along ocean margins and in basinal areas. Evidence from sediment tray experiments suggests that it may take several years for a stable community (including foraminifers) to become reestablished in small areas of defaunated sediment. Large devastated areas may require substantially longer to recover. However, on the Madeira Abyssal Plain, a normal foraminiferal assemblage occurs on the surface of a turbidite deposited several hundred years ago, suggesting that large-scale recolonization may occupy decades rather than centuries. The fossil foraminiferal assemblages present in deep-water flysch sequences are presumably the product of similar recolonization (?successional) events.These and other biological processes often operate on time scales (days, months, years) which usually can not be resolved in the stratigraphic record. This inevitably complicates the application of biological research to palaeontology.

Phytoplankton growth and Zooplankton grazing in oligotrophic oceans

Central oceanic regions such as the Sargasso Sea and the North Pacific Gyre have traditionally been thought of as biological deserts1,2. New phytoplankton production estimates3 and interpretations of physiological data4,5 have suggested that these areas are, in fact, highly productive and that nutrient exchanges supporting these high growth rates are extremely transient. Fast phytoplankton growth rates must be balanced by equally fast zooplankton-caused mortality. Zooplankton abundances and their filtration rates, however, are consistent with slow phytoplankton growth rates, not fast. It is shown here that the dominant grazers in oligotrophic areas seem to be microzooplankton, and that molecular diffusion limits the effect of nutrient pulses, implying that bulk nutrient concentrations are most important. Present growth studies imply that phytoplankton can meet their growth needs with nanomolar ammonia concentrations.

Petroleum Prospects of the Deep Offshore

A rough general assessment of the possibilities of petroleum accumulations in deep ocean regions beyond the continental shelf has been undertaken, for convenience, under three major heads--the central ocean region, the continental margin region, and the small ocean basins region. The information used comes largely from marine geophysical surveys and from 417 holes of the Deep Sea Drilling Project. Evaluation is based principally on thickness of sediments, organic carbon content, reservoir rocks, probability of accumulation traps, probable geologic history, and known occurrences of oil and gas. The distinction is made between environment-accordant sediments (formed under essentially the same geomorphic conditions as at their sites today) and environment-discordant sediments (formed under markedly different conditions). The central ocean region is considered with respect to the sedimentary rock developments of each of its major geomorphic units. In general, the prospects for petroleum accumulations appear unfavorable because of thinness of sediments, low organic carbon content, scarcity of reservoirs, paucity of shows, and generally horizontal attitude militating against trapping conditions; however, there are some exceptional areas. The continental margin region includes (1) marginal geosynclines, (2) outer-margin aprons, (3) marginal-plateau blocks, (4) marginal-trench fillings, (5) continent-related deep water fans, and (6) transmarginal ridges. The region as a whole has favorable aspects as regards thickness of sediments, source rocks, reservoirs, sealing rocks, petroleum shows, geologic history, and probability of traps. In the small ocean basins, thick sedimentary sections, abundant terrestrial and marine organic matter, reducing bottom conditions, well-developed reservoirs, mobile tectonic environment, and commonly an abundance of evaporites and diapiric structures combine to give a very favorable rating, supported by prolific production from the borders of many of these basins. With respect to production prospects, the deep offshore has obvious handicaps of unfavorable environment and costly operations, but where economic prospects are sufficiently good, the technological challenge can be met. There are large, almost untouched areas of deep offshore, sufficiently prospective to justify exploratory drilling, that urgently need evaluation. The United States alone has more than 1.5 million sq mi (3.9 million sq km) of combined shelf and deep-water offshore over which it can rightfully claim jurisdiction, of which only about 2% has ever been leased for development.