Planktonic Foraminifera Globigerinoides Sacculifer Research Articles

Equatorial Atlantic sea surface temperature for the last 30 kyr: A comparison of U37k′, δ18O and foraminiferal assemblage temperature estimates

A recently developed technique for determining past sea surface temperatures (SST), based on an analysis of the unsaturation ratio of long chain C37 methyl alkenones produced by Prymnesiophyceae phytoplankton (U37k′), has been applied to an upper Quaternary sediment core from the equatorial Atlantic. U37k′ temperature estimates were compared to those obtained from δ18O of the planktonic foraminifer Globigerinoides sacculifer and of planktonic foraminiferal assemblages for the last glacial cycle. The alkenone method showed 1.8°C cooling at the last glacial maximum, about 1/2 to 1/3 of the decrease shown by the isotopic method (6.3°C) and foraminiferal modern analogue technique estimates for the warm season (3.8°C). Warm season foraminiferal assemblage estimates based on transfer functions are out of phase with the other estimates, showing a 1.4°C drop at the last glacial maximum with an additional 0.9°C drop in the deglaciation. Increased alkenone abundances, total organic carbon percentage and foraminiferal accumulation rates in the last glaciation indicate an increase in productivity of as much as 4 times over present day. These changes are thought to be due to increased upwelling caused by enhanced winds during the glaciation. If U37k′ estimates are correct, as much as 50–70% (up to 4.5°C) of estimated δ18O and modern analogue temperature changes in the last glaciation may have been due to changes in thermocline depth, whereas transfer functions seem more strongly influenced by seasonality changes. This indicates these estimates may be influenced as strongly by other factors as they are by SST, which in the equatorial Atlantic was only reduced slightly in the last glaciation.

Holocene Oxygen and Carbon Isotopic Records of Core OR102-3off Southeastern Taiwan:Paleoceanographic Implications

The Holocene carbon and oxygen isotopic records of the planktonic foraminifera Globigerinoides sacculifer from core OR102-3 off southeastern Taiwan are presented. The isotopic values for this taxon from the Holocene period show ranges from -2.45‰ to -1.70‰ for δ^(18)O and from 2.47‰to 1.72‰ for δ^(13)C, respectively. Paleo-temperatures revealed from transfer function estimates of foraminifera assemblages in this core and in nearby core OR216-17 show that the surface waters in this region remained relatively warm and constant during the Holocene. The δ^(18)O values of the surface seawaters overlying the two core locations during the Holocene were then calculated using the paleotemperature equation. Results show that oxygen isotopic variations of the local surface waters during the Holocene were within 1‰ for core OR102-3 and 0.5‰ for core OR216-17, respectively. Two freshwater spikes are detected for core OR102-3 at about 2400yrs B.P. and 5700yrs B.P., but these spikes are not found in core OR216-17. These two freshwater spikes may be related to precipitation increases over eastern Taiwan during those two periods. Carbon isotopic records indicate that the δ^(13)C of the total dissolved CO^(2) in surface waters were almost the same for both cores during the Holocene.

Morphological and physiological responses of Globigerinoides sacculifer (Brady) under varying laboratory conditions

The planktonic foraminifer Globigerinoides sacculifer (Brady) was maintained in the laboratory under different temperature (19.5–29.5°C) and salinity (33 and 36‰) regimes. The light and feeding conditions were adjusted to the open ocean environment. The light intensity and quality corresponded to a water depth of 10–30 m and the specimens were fed daily. Specimens were raised from a mean initial size of approximately 220–240 μm to the reproductive mean size ranging from 521 μm to 657 μm according to the different temperature and salinity regimes. The survival time decreased with increasing temperature relatively independent of salinity. The growth rate decreased with decreasing temperatures but significantly only at the lowermost temperature range. The general vitality increased with increasing salinity, partially indicated by more chamber formations of specimens of the 36‰ salinity group in comparison to those of the 33‰ salinity group. The different phenotypes of the final chamber and the different morphologies of G. sacculifer are discussed.

Effects of temperature and salinity on the growth and survival of the planktonic foraminifer Globigerinoides sacculifer: Caron, D.A., W.W. Faber Jr. and A.W.H. Bé, 1987. J. mar. biol. Ass. U.K., 67(2):323–341

Effects of temperature and salinity on the growth and survival of the planktonic foraminifer Globigerinoides sacculifer: Caron, D.A., W.W. Faber Jr. and A.W.H. Bé, 1987. J. mar. biol. Ass. U.K., 67(2):323–341

An estimation of calcium carbonate deposition rate in a planktonic foraminifer Globigerinoides sacculifer using 45 Ca as a tracer; a recommended procedure for improved accuracy

An estimation of calcium carbonate deposition rate in a planktonic foraminifer Globigerinoides sacculifer using 45 Ca as a tracer; a recommended procedure for improved accuracy

Sequence of Morphological and Cytoplasmic Changes during Gametogenesis in the Planktonic Foraminifer Globigerinoides sacculifer (Brady)

The formation of a saclike chamber in individuals of Globigerinoides sacculifer in a laboratory culture signals impending gametogenesis. The earliest phase of gametogenesis starts with gradual shortening of the spines at midday and complete shedding of spines toward midnight. Concurrently, the symbiotic dinoflagellates are lysed and most likely digested and their remains expelled by their foraminiferal host. Fine structure evidence shows the initiation of nuclear division and development of large vacuoles within the cytoplasm. From midnight to 0700, continued nuclear division and expansion of the vacuoles and lacunae between the nucleated masses of cytoplasm cause the cytoplasm to fill the saclike chamber and cytoplasmic bulges to emerge from the shell's apertures. Gamete release occurs usually between 0900 and 1600, peaking at 1200 and 1300. The synchronous developmental sequence of gametogenesis in G. sacculifer may be of adaptive significance for greater potential fertilization in these holoplanktonic organisms. Sequence of morphological and cytoplasmic changes during gametogenesis in the planktonic foraminifer Globigerinoides sacculifer (Brady)

Effects of variations in light intensity on life processes of the planktonic foraminifer Globigerinoides sacculifer in laboratory culture

The planktonic foraminifer Globigerinoides sacculifer (Brady) was cultured under two different light intensities and in continuous darkness. High light intensity (HLI = 400–500 μeinsteins/m2/s) resulted in a longer lifespan, a greater number of chambers formed, and a larger final shell size compared with individuals cultured under low light intensity (LLI = 20–50 μeinsteins/m2/s) or in continuous darkness. Shell growth rates were unaffected by increasing light intensity, but gametogenesis was delayed. Continuous darkness induced a rapid onset of gametogenesis in organisms with shell lengths larger than 250 μm. Feeding frequency had a greater effect on growth and reproduction than light intensity under conditions of LLI and HLI, but continuous darkness had an overriding effect on growth and reproduction owing to the rapid onset of gametogenesis which terminated the life of the mother cell. Our previous data indicated that the longevity of G. sacculifer was dependent on feeding frequency, and that G. sacculifer cultured under LLI had a lifespan of approximately 2–4 weeks. Present results suggest that the lifespan can vary from a minimum of 8 days for organisms fed daily in continuous darkness to a maximum of 54 days for organisms fed once every 7 days and maintained in HLI. It is concluded that individual G. sacculifer attain a shell size greater than 600 μm only if they maintain their position in the euphotic zone. Prolonged existence below the euphotic zone would result in premature death or gametogenesis following stunted shell growth.

Isotopic and biostratigraphical records of calcareous nannofossils in a Pleistocene core

Knowledge of the species composition is essential for the isotopic record of polyspecific coccolith assemblages in deep-sea sediments to be interpreted properly. We have determined the carbon and oxygen isotopic composition as well as the relative abundance of coccolith species on the 3–25 µm fractions of the Caribbean core P6304-4. The dominant taxon in all samples is well-preserved Gephyrocapsa spp. Oxygen isotope variations clearly define glacial–interglacial oscillations. Except in the upper part of the core, carbon isotopic compositions are not related to the oxygen isotope stratigraphy. The occurrence of three coccolith datum levels in the core correlates almost exactly with globally-synchronous horizons1. The amplitude of the coccolith δ18O record (2.4‰) is significantly greater than that for the planktonic foraminifera Globigerinoides sacculifer in P6304-4 and adjacent cores2–4. We suggest here that selective dissolution or deep calcification during interglacials reduced the amplitudes of G. sacculifer in these cores and that the coccolith record is a more reliable indicator of temperature and δ18O changes in surface seawater.