12 research outputs found
Lake Kivu expedition : geophysics, hydrography, sedimentology (preliminary report)
In March 1971, seven members of the Woods Hole Oceanographic Institution
were engaged in a multidisciplinary study of Lake Kivu. This expedition represents
part of a long-range program concerned with the structural and hydrographical
settings of the East African Rift Lakes and their relationships to
the Red Sea and the Gulf of Aden Rifts. The program started in May 1963 with
a geophysical study on Lake Malawi (von Herzen and Vacquier, 1967). Several
expeditions of our Institution into the Red Sea and Gulf of Aden area in 1964,
1965 and 1966 (Degens and Ross, 1969) provided detailed geological information
on the "northern" extension of the East African Rift. And finally our study of
last year on Lake Tanganyika c1osed a major gap in the program; it allowed
us to out1ine a model on the evolution of a rift which starts with (i) bulging
of the earth's crust, (ii) block-faulting, (iii) volcanism and hydrothermal
activity, and which has its final stage in (iv) sea floor spreading (Degens
et al. 1971). In the case of Lake Tanganyika, only the second stage of this
evolution series has been reached, i.e. block-faulting. In contrast, the Red
Sea and the Gulf of Aden had already evolved to active sea floor spreading, almost
25 million years ago. Somewhere along the line between Lake Tanganyika
and the Gulf of Aden must lie the "missing link" of this evolution series.
Lake Kivu, almost 100 miles to the north of Lake Tanganyika is situated
at the highest point of the Rift Valley and is surrounded by active volcanoes
and geothermal springs. As recently as 1944, lava flows reached the lake
shore. This lake was therefore, a natural choice to test our hypothesis on
the origin and development of rifts. Furthermore, the occurrence of large
quantities of dissolved gases, e.g., CO2 and methane, represented an interesting
geochemical phenomenon worthwhile to investigate.Supported by the National Science Foundation
with Grants GA 19262, GB 20956, and GU 3927;
grants from the Petroleum Research Fund of
the American Chemical Society PRF#1943A2;
and by private research funds of the Woods
Hole Oceanographic Institution
Oxygen flux in surface sediments (Table 1)
Over the past decade an increasing body of evidence has accumulated indicating that much, perhaps most, of the deep sea floor is an environment of substantial temporal variability (Smith and Baldwin, 1984 doi:10.1038/307624a0; Smith, 1987; Deuser and Ross, 1980 doi:10.1038/283364a0; Thiel et al., 1988). This variability is driven largely by seasonal changes of processes occurring in the surface waters (Smith, 1987; Deuser and Ross, 1980; Billett et al., 1983 doi:10.1038/302520a0). The coupling of the deep sea floor environment to the surface waters is the result of rapid vertical transport of particulate matter through the water column (Honjo, 1982 doi:10.1126/science.218.4575.883; Deuser et al., 1986 doi:10.1016/0198-0149(86)90120-2; Lampitt, 1985 doi:10.1016/0198-0149(85)90034-2), affording only limited time for degradation before arrival at the sea floor. Studies in the Pacific Ocean have indicated that temporal variations in particulate organic carbon fluxes to the sea floor are accompanied by temporal variability in sediment oxygen demand by as much as a factor of four (Smith and Baldwin, 1984; Smith, 1987). We report here time-series studies of oxygen fluxes into the sediments of the oligotrophic Atlantic near Bermuda which contrast sharply with these previous reports. At the Bermuda site, despite large seasonal variations in particulate organic carbon fluxes, in situ measured sediment oxygen consumption does not vary significantly. These results imply that large areas of the sea floor may be characterized by seasonally invariant sediment oxygen demand
The Conch of Limacina and Peraclis (Pteropoda) and a Model for the Evolution of Planktonic Gastropods
Pteropod shell morphologies can be explained by neotenic extension of larval features observed in benthic forms, such as the sinistral coiling of Architectonacea and the ornamentation patterns of Tonnacea, into the adult shell of permanently planktonic living snails. Presented models suggest derivation of pteropods from primitive prosobranch mesogastropods of the Late Paleozoic, rather than from opistobranchs
Biogenic opal, carbonate fluxes, time series
Analyses of samples from a 14-year series of sediment-trap deployments in the deep Sargasso Sea reveal a significant trend in the ratio of the sinking fluxes of biogenic calcium carbonate and silica. Although there are pronounced seasonal cycles for both flux components, the overall opal/CaCO3 ratio changed by 50% from 1978 to 1991 (largely due to a decrease of opal flux), while total flux had no significant trend. These results suggest that plankton communities respond rapidly to subtle climate change, such as is evident in regional variations of wind speed, precipitation, wintertime ventilation and midwater temperatures. If the trends we observe in the makeup of sinking particulate matter occur on a large scale, they may in turn modify climate by modulating ocean-atmosphere CO2 exchange and albedo over the ocean
Marine Isotope Stage 3 sea level fluctuations: data synthesis and new outlook
To develop a better understanding of the abrupt Dansgaard-Oeschger mode of climate change, it is essential that we establish whether the ice sheets are actively involved, as trigger or amplifier, or whether they merely respond in a passive manner. This requires careful assessment of the fundamental issues of magnitude and phasing of global ice volume fluctuations within marine isotope stage 3 (MIS 3), which to date remain enigmatic. We review recent advances in observational studies pertaining to these key issues and discuss the implications for modeling studies. Our aim is to construct a robust stratigraphic framework for the MIS 3 period regarding sea level variability, using the most up-to-date arguments available by combining insights from both modeling and observational approaches