Diversity of atlantic coastal plain mollusks since the pliocene

About 70 percent of tropical western Atlantic mollusk species have become extinct since the Pliocene, which has led to perceptions of a corresponding decline in diversity. However, a compilation of gastropod species from Plio-Pleistocene faunas of the United States Atlantic coastal plain and from Recent western Atlantic faunas indicates that regional diversity has not changed since the Pliocene. Gastropod diversity in the Pliocene Pinecrest Beds in Florida approximates that seen today on either coast of Florida. Gastropod diversity is not demonstrably different in the Recent tropical western Atlantic than in the Recent tropical eastern Pacific. High extinction rates must have been balanced by high origination rates.     

Foraminifera and chlorophyll maximum: vertical distribution, seasonal succession, and paleoceanographic significance

Many planktonic foraminiferal species deposit their shells at the chlorophyll maximum zone, and it is the temperature range here that is relevant to oceanographic models which use ratios of oxygen-18 to oxygen-16 in fossil foraminifera and foraminiferal fossil assemblages to ascertain past climates. During periods of stratification of the upper water column, the temperature at the chlorophyll maximum may differ from the sea surface temperature by 10 degrees C in the western North Atlantic.     

Reduced competition and altered feeding behavior among marine snails after a mass extinction

Extinction may alter competitive interactions among surviving species, affecting their subsequent recovery and evolution, but these processes remain poorly understood. Analysis of predation traces produced by shell-drilling muricid snails on bivalve prey reveals that species interactions were substantially different before and after a Plio-Pleistocene mass extinction in the western Atlantic. Muricids edge- and wall-drilled their prey in the Pliocene, but Pleistocene and Recent snails attacked prey only through the shell wall. Experiments with living animals suggest that intense competition induces muricid snails to attack shell edges. Pliocene predators, therefore, probably competed for resources more intensely than their post-extinction counterparts.     

Dust concentration in the atmosphere of the equatorial north atlantic: possible relationship to the sahelian drought

The concentration of insoluble mineral aerosol in the lower troposphere of the western equatorial North Atlantic Ocean has increased by a factor of 3 over the last decade. This increase may be related to the drought in the Sahelian zone of North Africa.     

Deep-Sea coral evidence for rapid change in ventilation of the deep north atlantic 15,400 years Ago

Coupled radiocarbon and thorium-230 dates from benthic coral species reveal that the ventilation rate of the North Atlantic upper deep water varied greatly during the last deglaciation. Radiocarbon ages in several corals of the same age, 15.41 +/- 0.17 thousand years, and nearly the same depth, 1800 meters, in the western North Atlantic Ocean increased by as much as 670 years during the 30- to 160-year life spans of the samples. Cadmium/calcium ratios in one coral imply that the nutrient content of these deep waters also increased. Our data show that the deep ocean changed on decadal-centennial time scales during rapid changes in the surface ocean and the atmosphere.     

Radon-222 in the North Atlantic trade winds: its relationship to dust transport from Africa

The concentration of radon-222 in air was measured during a flight from Miami to Barbados to Dakar and return; concentrations ranged from 1 to 55 picocuries per standard cubic meter of air and were highest in areas of dense haze, which were present along most of the flight path across the Atlantic Ocean. The haze is attributed to dust originating from the arid regions of western Africa. Radon-222 may be useful as a tracer for African air parcels over the equatorial Atlantic.     

Younger dryas age advance of franz josef glacier in the southern alps of new zealand

A corrected radiocarbon age of 11,050 +/- 14 years before present for an advance of the Franz Josef Glacier to the Waiho Loop terminal moraine on the western flank of New Zealand's Southern Alps shows that glacier advance on a South Pacific island was synchronous with initiation of the Younger Dryas in the North Atlantic region. Hence, cooling at the beginning of the Younger Dryas probably reflects global rather than regional forcing. The source for Younger Dryas climatic cooling may thus lie in the atmosphere rather than in a North Atlantic thermohaline switch.     

Orbitolina, a cretaceous larger foraminifer, from flemish cap: paleoceanographic implications

The Tethyan larger foraminiferal genus Orbitolina has been found in the easternmost part of the western North Atlantic continental shelf at 46 degrees 30'N. All other known occurrences of the genus in North America are south of 33 degrees N. The species is Orbitolina conoidea Gras; its abundance in a grainsupported limestone indicates a tropical neritic environment and precludes the influence of Arctic waters in the Flemish Cap region in Early or Middle Cretaceous times.     

Caribbean reef development was independent of coral diversity over 28 million years

The relationship between natural variations in coral species diversity, reef development, and ecosystem function on coral reefs is poorly understood. Recent coral diversity varies 10-fold among geographic regions, but rates of reef growth are broadly similar, suggesting that diversity is unimportant for reef development. Differences in diversity may reflect regional differences in long-term biotic history in addition to environmental conditions. Using a combination of new and published fossil and stratigraphic data, we compared changes in coral diversity and reef development within the tropical western Atlantic over the past 28 million years. Reef development was unrelated to coral diversity, and the largest reef tracts formed after extinction had reduced diversity by 50%. High diversity is thus not essential for the growth and persistence of coral reefs.     

Natal homing and connectivity in Atlantic bluefin tuna populations

Atlantic bluefin tuna populations are in steep decline, and an improved understanding of connectivity between individuals from eastern (Mediterranean Sea) and western (Gulf of Mexico) spawning areas is needed to manage remaining fisheries. Chemical signatures in the otoliths of yearlings from regional nurseries were distinct and served as natural tags to assess natal homing and mixing. Adults showed high rates of natal homing to both eastern and western spawning areas. Trans-Atlantic movement (east to west) was significant and size-dependent, with individuals of Mediterranean origin mixing with the western population in the U.S. Atlantic. The largest (oldest) bluefin tuna collected near the northern extent of their range in North American waters were almost exclusively of western origin, indicating that this region represents critical habitat for the western population.     

Benthic storms: temporal variability in a deep-ocean nepheloid layer

Time series measurements of light scattering were made for 2(1/2) months at 20 meters above the bottom in the western North Atlantic. The highest values recorded with the nephelometer exceeded all previous measurements worldwide. Rapid changes indicated a high degree of activity near the sea floor, and some increases may have been related to atmospheric storms.     

Erratum

Because of an error in the program used to calculate the volume of cylinders, the egg volumes for pomacentrins reported by R. E. Thresher (1 Oct. 1982, p. 70) were uniformly too large by a factor of 4. In figure 1 (p. 71), the scale on the abscissa for the size-frequency distribution of pomacentrin eggs should be 0 to 1.0 cubic millimeters, rather than 0 to 4.0 mm(3), and the average egg volumes for western Atlantic and western Pacific species are, respectively, 0.165 mm(3) and 0.46 mm(3). The error affects neither the distributions of egg volumes in the two areas nor the magnitude nor significance level of the differences between them.     

Foraminifera: distribution of provinces in the Western north atlantic

All published distributional data on recent benthic foraminifera of the North American Atlantic continental margin were archived into computerized catalogs. Cluster analysis of these data delimited seven large, marginally overlapping provinces exhibiting a congruous relationship with western North Atlantic water masses. The single major latitudinal faunal change occurs at Cape Hatteras.     

The ocean: a natural source of carbon monoxide

The surface waters of the western Atlantic are supersaturated with respect to the partial pressure of carbon monoxide in the atmosphere. Under these conditions, the net transport of carbon monoxide across the air-sea interface must be from the sea into the atmosphere. Thus, the ocean appears to act as a source of carbon monoxide. The ocean may be the largest known natural source of this gas, contributing possibly as much as 5 percent of the amount generated by burning of fuels by man.     

Determining the general circulation of the oceans: a preliminary discussion

The classical oceanographic problem of deducing the unknown constant in the dynamic method-the problem of the "level of no motion"-may be treated as a geophysical inverse problem. The unknown "barotropic" velocity may be chosen to satisfy an arbitrary number of conservation laws, subject to perfect geostrophic balance and with explicit use made of the relative errors in the observations. The solution obtained is one of minimum energy. A western North Atlantic region is used to demonstrate the power of the method.     

Neotropical mammals and the myth of amazonian biodiversity

Data were compiled on the distribution of mammal taxa (883 species, 242 genera, 45 families, and 10 orders) among South America's six major macrohabitats: lowland Amazon forest, western montane forests, Atlantic rain forest, upland semideciduous forest, southern mesophytic forest, and drylands. The drylands are the richest area in numbers of species supported and are more diverse than the other habitats, including the lowland Amazon rain forest, when endemics are considered. An analysis of number of endemic and nonendemic taxa versus size of area found a simple positive linear relationship: the drylands, almost twice as extensive as the Amazon lowlands, support more endemic taxa. Conservation plans that emphasize the wet tropics and fail to consider the drylands as special repositories of mammal diversity will be unable to preserve a significant number of novel taxa.     

Paleocirculation of the deep north atlantic: 150,000-year record of benthic foraminifera and oxygen-18

Benthic foraminiferal faunas in a piston core from 3331 meters at 44 degrees N on the Mid-Atlantic Ridge show striking variations in the relative abundance of species. Uvigerina peregrina, which is broadly distributed today in the South Atlantic and in the Pacific in water that has been long isolated from the surface, is absent in the North and Equatorial Atlantic at depths occupied by highly oxygenated North Atlantic deep water. This species dominated the fauna at this site for much of the past 150,000 years. It is suggested that North Atlantic deepwater production was much reduced or eliminated at times of Uvigerina peregrina abundance, as a result of cooling and stratification of the Norwegian Sea surface, coincident with the times of the southward migration of the polar front in the North Atlantic.     

气候变化对西南大西洋渔业生态系统的影响研究进展

西南大西洋是世界重要的渔区之一，捕捞国家包括阿根廷等西南大西洋沿海国以及中国、日本等众多非沿海国家，其中阿根廷滑柔鱼（Illex argentinus）、阿根廷无须鳕（Merluccius hubbsi）、巴西小沙丁鱼（Sardinella brasiliensis）与弗氏绒须石首鱼（Micropogonias furnieri）是西南大西洋年均产量最高的4种主要经济渔获物。探究气候变化对西南大西洋生态系统的影响有利于建立基于生态系统的渔业资源保护与利用格局。本文从渔业资源与生态系统两个角度出发，分别归纳了生态系统的生物因子（主要经济渔获物）、非生物因子（环境因素）与营养结构（食物链和食物网）对气候变化的响应情况。分析认为，在今后探究西南大西洋生态系统对气候变化的响应的研究中，选取代表物种表征生态系统的变化并结合人类活动与气候变化的影响可以丰富生态系统的相关结论，为西南大西洋海域提供基于生态系统的科学管理策略。     

Internal waves: measurements of the two-dimensional spectrum in vertical-horizontal wave number space

Thermistor chain measurements of internal wave motions below the thermocline in the western North Atlantic have been spectrally decomposed in vertical-horizontal wave number space. The measured two-dimensional spectrum exhibits a systematic deviation from the corresponding Garrett and Munk model for internal wave spectra.     

Indian-atlantic transfer of thermocline water at the agulhas retroflection

During November and December 1983, two anticyclonic eddies were observed west of the Agulhas Retroflection, apparently spawned at the retroflection. The western eddy, centered 300 kilometers southwest of Cape Town, has a winter cooled core encircled by warm Indian Ocean water. Between Cape Town and the "Cape Town Eddy" is a net geostrophic transport of Indian Ocean thermocline water (14 x 10(6) cubic meters per second) into the South Atlantic Ocean. This circulation configuration, similar to that observed by earlier researchers, suggests that Indian-Atlantic thermocline exchange is a common occurrence. Such a warmwater link between the Atlantic and Indian oceans would strongly influence global climate patterns. The Indian Ocean water is warmer than the adjacent South Atlantic water and thus represents a heat input of 2.3 x 10(13) to 47 x 10(13) watts into the Atlantic. The large uncertainty arises from the unknown partition between two possible routes for the return flow from the Atlantic to the Indian Ocean: cooler South Atlantic thermocline water or much colder North Atlantic Deep Water. In either case, interocean mass and heat exchange of thermocline water at the Agulhas Retroflection is a distinct likelihood.