Modern planktic foraminifera

Planktic foraminifers are marine protozoans with calcareous Shells and chambered tests. They first appeared in the mid-Jurassic and spread since the mid-Cretaceous over all the world’s oceans. Modern planktic foraminifers evolved since the early Tertiary, when the first spinose species occurred. Most species live in the surface to sub-thermocline layer of the open ocean, and in marginal seas like the Mediterranean, Caribbean, South China Sea, and Red Sea. Planktic foraminifers are absent in shallow marginal seas, for example, the North Sea. Planktic foraminifers respond to food, temperature and chemistry of the ambient seawater. Species abundance varies according to seasons, water masses, and water depths. Symbiont-bearing species depend on light and are restricted to the euphotic zone. Planktic foraminifers constitute a minor portion of total Zooplankton, but are major producers of marine calcareous particles (shells) deposited on the ocean floor where they form the so-called foraminiferal ooze.Planktic foraminifers contribute substantially to the fossil record of marine Sediments and are of high ecologic, paleoceanographic, and stratigraphic significance since the mid-Cretaceous. Radiocarbon (14C) gives an absolute age of shell formation within late Pleistocene and Holocene Sediments. Factors that determine the modern faunal composition are applied to Interpretation of the fossil assemblages, for example, by multiple regression techniques (transfer functions) to yield an estimate on ancient environmental parameters. The chemical composition of the calcareous shell (stable isotopes and trace elements) holds clues to the chemical and physical State of the ambient seawater and is useful in the reconstruction of temperature, chemical State, and biological productivity of the ancient marine environment

Occurrence of pteropods in a deep eastern Arabian Sea core: Neotectonic implications

This paper reports pteropod shells (aragonitic) at 100, 200, 270-277 and 470 cm sediment depths in a core (EAST) recovered from 3820 m deep water from the eastern Arabian Sea. Ages of the four stratigraphic levels showing pteropod presence are estimated as 29, 52, 70-72 and 127 kyr. In normal circumstances microfaunal assemblages of this core are expected to be devoid of pteropod shells because the site is situated far below (∼ 3.5 km) the Aragonite Compensation Depth. Therefore, the recorded pteropod shells are exotic to the location and may have been transported from the shallower depths by the turbidity currents. The plausible reason for the preservation of aragonitic shells at such greater depth appears to be quick burial of pteropods resulting from large-scale vigorous slumping triggered by neotectonic activity

High-resolution study of planktic foraminifera from the eastern Mediterranean over the last 13 cal ka BP

A unique high-resolution record from the Nile prodelta has been investigated in order to study past hydrological and climatic changes in the southeastern Levantine region over the last 13 cal ka BP. To this end, we used planktic foraminifera (accumulation rates, diversity, assemblages and size properties) as bioindicators of the ecological characteristics of the water column (temperature, salinity, primary production and hydrology). These characteristics were mainly connected to Nile discharges and thermohaline circulation which in turn were controlled by various global and regional climatic forcing factors (e.g., orbital forcing, African and Indian Monsoon, North Atlantic Oscillation (NAO)). Our data showed seven main climatic periods: 1) from 13.0 to 11.5 cal ka BP encompassing the Younger Dryas and characterized by rather cold productive and mixed waters; 2) from 11.5 to 10.1 cal ka BP matching the start of the Holocene and the onset of the African Humid Period (AHP). This period was defined by surface water warming and increasing stratification due to increased river outflow; 3) from 10.1 to 6.4 cal ka BP encompassing the Sapropel deposit (S1) and matching the maximum of the AHP with drastic ecological conditions and maximum water stratification. During this period, the dominant warm taxon Globigerinoides ruber increased significantly in size and accumulation rate marking an opportunistic behavior and a total adaptation to the less saline and stratified waters. After 8.8 cal ka BP, the increase in diversity marked a progressive return to normal conditions; 4) from 6.4 to 2.9 cal ka BP, a progressive aridification period was recorded and the planktic ecosystem returned progressively to equilibrium conditions due to the recovery of thermohaline circulation after S1 and the decrease in Nile runoff; 5) from 2.9 to 1.1 cal ka BP, particular dry conditions were recorded leading to a severe drop in planktic diversity. These conditions seemed to be connected to a negative state of the NAO marking the Roman Humid Period in the western Mediterranean and being anti-phased with the southeastern Mediterranean; 6) from 1.1 to 0.54 cal ka BP, a humid period was recorded matching the Medieval Warm Anomaly and this time connected to a positive NAO. The highest foraminiferal diversity was recorded and the increase in proportions of deep dwellers and eutrophic taxa marked highly productive and mixed waters; 7) from 0.54 cal ka BP to modern time encompassing the Little Ice Age and recorded in our data by a general aridity and surface water warming

Response of benthic foraminifera to ocean acidification in their natural sediment environment: a long-term culturing experiment

Calcifying foraminifera are expected to be endangered by ocean acidification, However, the response of a complete community kept in natural sediment and over multiple generations under controlled laboratory conditions has not been constrained to date. During 5 six month incubation, foraminiferal assemblages were treated with pCO2 enriched seawater of 430, 907, 1865 and 3247 μatm pCO2. The fauna was dominated by Ammonia aomoriensis and Elphidium species, whereas agglutinated species were rare. After 6 months incubation, pore water alkalinity was much higher in comparison to the overlying seawater. Consequently, the saturation state of Òcalc was much higher in the sedi10 ment than in the water column in all pCO2 treatments and remained close to saturation. As a result, the life cycle of living assemblages was largely unaffected by the tested pCO2 treatments. Growth rates, reproduction and mortality, and therefore population densities and size-frequency distribution of Ammonia aomoriensis varied markedly during the experimental period. Growth rates varied between 25 and 50 μm per month, 15 which corresponds to an addition of 1 or 2 new chambers per month. According to the size-frequency distribution, foraminifera start reproduction at a diameter of 250 μm. Mortality of large foraminifera was recognized, commencing at a test size of 285 μm at a pCO2 ranging from 430 to 1865 μatm, and of 258 μm at 3247 μatm. The total organic content of living Ammonia aomoriensis has been determined to be 4.3% of dry 20 weight. Living individuals had a calcium carbonate production rate of 0.47 gm−2 yr−1, whereas dead empty tests accumulated at a rate of 0.27 gm−2a−1. Although Òcalc was close to 1, some empty tests of Ammonia aomoriensis showed dissolution features at the end of incubation. In contrast, tests of the subdominant species, Elphidium incertum, stayed intact. This species specific response could be explained by differences in 25 the elemental test composition, in particular the higher Mg-concentrations in Ammonia aomoriensis tests. Our results emphasize that the sensitivity to ocean acidification of endobenthic foraminifera in their natural sediment habitat is much lower compared to the experimental response of specimens isolated from the sediment

Pre-orbiter Investigation Final Report

Analysis of photographic mapping system for Lunar Orbiter progra

Organic carbon losses measured by heterotrophic activity of mesozooplankton and CaCO3 flux in the bathypelagic zone of the Arabian Sea

Organic carbon requirements for metabolisms of mesozooplankton in the bathypelagic zone were calculated for two stations (Western Arabian Sea Sediment Trap, WAST, 16°N 60°E, and Central Arabian Sea Sediment Trap, CAST, 14°N 64°E) and two different intermonsoonal periods (October 1995 and April 1997) in the Arabian Sea. These requirements were compared with inputs of particulate organic carbon (POC) measured from sediment traps. The temporal variability of POC flux is compared to the CaCO3 flux made up by planktic foraminiferans and coccolithophorids. The potential oxygen requirement of mesozooplankton was measured by the electron transport system (ETS) activity and the organic carbon demand calculated using conversion factors from the literature. Particulate CaCO3 flux was calculated from multinet hauls and sediment trap samples. Mesozooplankton organic carbon demand in the zone between 1050 and 3000 m differed locally and seasonally. At WAST, the mesozooplankton required 1778 μg C m−2 d−1 in October and only 484 μg C m−2 d−1 in April. At CAST, the respective values were 997 and 211 μg C m−2 d−1. No differences between the stations and time periods were discernible for the zone between 3000 and 3900 m at CAST and between 3000 and 4000 m at WAST; the values ranged between 73 and 98 μg C m−2 d−1. The input measured by sediment traps was sufficient to cover the calculated requirements of the mesozooplankton. The flux of calcareous particles and the mesozooplankton carbon requirements showed a similar pattern of temporal variability. At CAST the planktic foraminiferal shell flux was 33.2 mg CaCO3 m−2 d−1 in October and only 5.9 mg CaCO3 m−2 d−1 at 3000 m depth in April. Flux data derived from multinet hauls are of the same order of magnitude as the sediment trap data and, as multinet data yield a high temporal and spatial resolution, they could serve as a measure for open-ocean particulate flux