Calcification depth of deep-dwelling planktonic foraminifera from eastern North Atlantic: evidence from stable oxygen isotope ratios of shells from plankton tows

<p>Stable oxygen isotopes (δ<sup>18</sup>O) of planktonic foraminifera are one of the most used tools to reconstruct environmental conditions of the water column. Since different species live and calcify at different depths in the water column, the δ<sup>18</sup>O of sedimentary foraminifera reflects to a large degree the vertical habitat and interspecies δ<sup>18</sup>O differences and can thus potentially provide information on the vertical structure of the water column. To fully unlock the potential of foraminifera as recorders of past surface water properties, it is necessary to understand how and under what conditions the environmental signal is incorporated into the calcite shells of individual species. Deep-dwelling species play a particularly important role in this context, since their calcification depth reaches below the surface mixed layer. Here we report δ<sup>18</sup>O measurements made on four deep-dwelling Globorotalia species collected with stratified plankton tows in the Eastern North Atlantic. Size and crust effects on the δ<sup>18</sup>O signal were evaluated showing that a larger size increases the δ<sup>18</sup>O of <em>Globorotalia inflata</em> and <em>Globorotalia hirsuta</em>, and a crust effect is reflected in a higher δ<sup>18</sup>O in <em>Globorotalia truncatulinoides</em>. The great majority of the δ<sup>18</sup>O values can be explained without invoking disequilibrium calcification. When interpreted in this way the data imply depth-integrated calcification with progressive addition of calcite with depth to about 300 m for <em>G. inflata</em> and to about 500 m for <em>G. hirsuta</em>. In <em>Globorotalia scitula</em>, despite a strong subsurface maximum in abundance, the vertical δ<sup>18</sup>O profile is flat and appears dominated by a surface layer signal. In <em>G. truncatulinoides</em>, the δ<sup>18</sup>O profile follows equilibrium for each depth, implying a constant habitat during growth at each depth layer. The δ<sup>18</sup>O values are more consistent with the predictions of the Shackleton (1974) paleotemperature equation, except in <em>G. scitula</em>, which shows values more consistent with the Kim and O’Neil (1997) prediction.  In all cases, we observe a difference between the level where most of the specimens were present and the depth where most of their shell appears to calcify.</p>

Late Neogene–Quaternary Planktic Foraminiferal Biostratigraphy and Biochronology from ODP Site 807A, Ontong Java Plateau, Western Equatorial Pacific

ABSTRACT A biostratigraphic and biochronological study from the late Neogene–Quaternary section of Ocean Drilling Program (ODP) Site 807A, located on the Ontong Java Plateau, western equatorial Pacific, revealed 50 planktic foraminiferal events, enabling the identification of eight late Neogene–Quaternary biozones, from the Globorotalia plesiotumida Interval Zone to the Globorotalia truncatulinoides Interval Zone. A significant faunal turnover (17 events) from late Pliocene identified in cores 7 and 8, between 70 and 55 meters below seafloor (mbsf), and spanning 0.67 million years (Myr). This noteworthy turnover may be the result of a shift in oceanographic conditions pertaining to the closure of the Indo–Pacific Seaway, followed by the Northern Hemisphere Glaciation. This study provides a high resolution biostratigraphic and biochronological framework for ODP Site 807A that will aid in correlation and timing the various paleoceanographic changes over the last 6 million years in the western equatorial Pacific.

Preservation potential assessment of central Atlantic biogenic carbonate deposits using X-ray micro-computed tomography (XMCT)

<p>Dissolution of foraminiferal calcite above the lysocline can occur within the water column, at the sediment-water interface, and/or within the sediment column as a result of low in-situ carbonate ion concentrations. The dissolution of foraminiferal shells, which are widely used for paleoceanographic studies, has the potential to influence the weight and the chemical composition of the whole test. Their partial dissolution has been suggested to significantly bias their δ<sup>18</sup>O and δ<sup>13</sup>C signals, while the trace element ratios decrease as dissolution progresses. Despite the significant Atlantic importance on the climate system, and that of the carbonate system on atmospheric CO<sub>2</sub> concentration, there have been only a few studies examining carbonate preservation along depth transects in the North and South Atlantic, and mostly by indirect means.</p><p>In order to assess the preservation potential of the central Atlantic basins, a set of 16 Atlantic surface sediment (core-top) samples along the mid-Atlantic Ridge was deployed. The samples span from approximately 30°N to 30°S and are situated along the mid-Atlantic Ridge from an average water depth of 3700 m, well above the 4200 m modern lysocline, with roughly equal bottom water ΔCO<sub>3</sub><sup>2−</sup> values (23 ±4 μmol/kg). Typically 15 pre-weighed shells of three different planktonic foraminifera species, widely used in paleoceanographic research, were picked from each sample (300-355 μm) and scanned using a GE vtomex s high-resolution micro-CT scanner. The species under consideration, namely <em>Globigerinoides ruber</em> s.s. (white), <em>Trilobatus trilobus</em> and <em>Globorotalia truncatulinoides</em>, inhabit different water depths and are known to have different geochemistries and thus preservation potentials. The preliminary analysis of the tomographs suggests that although carbonate sediments from the eastern basins below from the south equatorial upwelling zone are more corroded their initial geochemistry is not greatly altered by dissolution.</p>

BIOSTRATIGRAFI FORAMINIFERA KUARTER PADA BOR INTI MD 982152 DAN 982155 DARI SAMUDRA HINDIA

Dari bor inti pada EKSPEDISI IMAGES, di Samudra Hindia, telah diteliti sebanyak 21 percontoh sedimen dari lokasi MD 982152, dan 29 buah dari lokasi MD 982155 untuk kepentingan biostratigrafi berdasarkan analisis foraminifera plankton dalam interval 1,5 meter. Pada kedua penampang bor inti tersebut hanya dijumpai satu zona foraminifera plankton Kuarter, yaitu Zona Globorotalia truncatulinoides. Untuk MD 982152, zona ini bisa dibagi ke dalam dua subzona, yakni Subzona-subzona Globorotalia crassaformis hessi dan Globigerinella calida, sedangkan untuk MD 982155, zona tersebut bisa dibagi lagi ke dalam tiga subzona, yakni Subzona-subzona Globorotalia crassaformis hessi Globigerinella calida, dan Beella digitata. Kejadian yang signifikan di kedua penampang itu adalah Datum Pemunculan Pertama dari Globigerinella calida dan Pemunculan Akhir dari Globorotalia crassaformis hessi. Pada MD 982155, dijumpai Pemunculan Pertama dari Beella digitata. Kata kunci: foraminifera plankton, Kuarter, biostratigrafi, Samudra Hindia. From IMAGES Expedition in Indian Ocean, 21 samples from MD 982152, and 29 samples from MD 982155 had been studied for the purpose of biostratigraphy based on planktonic foraminifera within 1,5 meter interval. In both sections, only one Quaternary zone is found, namely Globorotalia truncatulinoides Zone. For MD 982152, that zone can be subdivided into two interval subzones e.g. Globorotalia crassaformis hessi and Globigerinella calida calida. However, in MD 982155 Globorotalia truncatulinoides Zone can be subdivided into three subzones namely, Globorotalia crassaformis hessi, Globigerinella calida calida, and Beella digitata Subzones. The planktonic foraminifera event revealed in both sections are the First Appearance Datum (FAD) of Globigerinella calida calida and the Last Appearance (LAD) of Globorotalia crassaformis hessi. In MD 982155 the FAD of Beella digitata is found. Keywords: planktonic foraminifera, Quaternary, biostratigraphy, Indian Ocean.

Exploring photosymbiotic ecology of planktic foraminifers from chamber-by-chamber isotopic history of individual foraminifers

Evolution of photosymbiotic ecology is an important adaptation for planktic foraminifers that enhances the ecological advantage of living in oligotrophic oceans. Therefore, detecting photosymbiotic ecology in fossil species is one of the keys to understanding the paleobiodiversity dynamics of planktic foraminifers. Because foraminiferal tests record the ontogenetic history of ecological information in geochemical signatures, analyzing individual geochemical profiles with growth can reveal a species’ ecology. This study examined chamber-by-chamber stable isotopes (δ13C and δ18O) of foraminiferal individuals to identify photosymbiotic signals. We observed an ontogenetic δ13C increase of up to 2.4‰, accompanied by relatively stable, negative δ18O, in the symbiotic species Globigerinoides conglobatus and Globigerinoides sacculifer. In contrast, δ13C and δ18O showed significant positive correlation during ontogeny in the asymbiotic species Globorotalia truncatulinoides. These two ecological groups produce contrasting isotopic profiles, thereby allowing us to use our ontogenetic isotopic analyses of individual specimens to identify algal photosymbiosis in fossil foraminifers. The chamber-by-chamber isotope analyses with individual ontogeny have great advantages in analyzing rare species because only one individual is required to describe ontogenetic isotopic history. In addition to photosymbiotic identification, our methods hold great potential to provide new insight into species paleoecological studies such as the ontogenetic history of calcification depth.