Data report: middle to late Pleistocene planktonic foraminifer abundances from IODP Holes U1431D, U1432C, and U1433A

The primary goal of this study is to assess the potential of International Ocean Discovery Program Expedition 349 Sites U1431, U1432, and U1433 for middle and late Pleistocene paleoceanographic reconstructions. For this, we recorded planktonic foraminifer abundances (tests/g of dry sediment) from the uppermost sections of Holes U1431D, U1432C, and U1433A. Our data suggest that Hole U1432C presents the highest potential for planktonic foraminifer–based paleoceanographic reconstructions. Planktonic foraminifer abundance fluctuations in sediments from Hole U1431D suggest that this hole is a good candidate to further investigate water-chemistry changes in paleoenvironmental reconstructions since the middle Pleistocene. Meanwhile, the absence planktonic foraminifers precludes the use of this proxy in reconstructions from Hole U1433A.


Introduction
During International Ocean Discovery Program (IODP) Expedition 349, five sites were drilled in the deep basin of the South China Sea (SCS) with the main objective to test hypotheses for timing and opening mechanisms of this marginal basin.Three of these sites (U1431-U1433) retrieved sediment from the northern East, central East, and Southwest Subbasins of the SCS following a north-south transect.Shipboard dating of microfossils indicated that the uppermost sediments recovered from these sites comprise the middle and upper Pleistocene.The location of these sites makes them of particular interest to examine paleoceanographic and sedimentary responses to regional climatic processes.
Planktonic foraminifers are widely used in paleoceanographic reconstructions because their abundance and biodiversity are controlled by surface hydrographic conditions (Jonkers and Kučera, 2015).Planktonic foraminifer test production and flux to the seafloor are mainly controlled by surface-water primary productivity (Jonkers and Kučea, 2015;Salmon et al., 2015).The production, transportation, deposition, and dissolution of carbonate forms a significant part of the global carbon cycle (Wang et al., 2016).In deep ocean basins, carbonate ion concentration (CO 3 -2 ) saturation controls carbonate preservation and sedimentary accumulation.The SCS has a deeper lysocline and carbonate compensation depth (CCD) (at ~3000 and 3500 meters below seafloor [mbsf], respectively) than the Western Pacific (Li et al., 2008).Thus, deep-sea sediments deposited in this marginal basin are potential archives for paleoceanographic studies.
Here we present planktonic foraminifer abundances from the middle and upper Pleistocene of Holes U1431D, U1432C, and U1433A.The primary objective of this study is to present the overall abundances of planktonic foraminifers and to provide a first assessment of the potential of these sites for middle and late Pleistocene planktonic foraminifer-based paleoceanographic reconstructions.

Geological setting
The SCS is a large marginal sea in the Western Pacific with a deep central basin (2000-4700 meters below sea level) divided into the Northwestern, East, and Southwest Subbasins (see the Expedition 349 summary chapter [Li et al., 2015]).The East and Southwest Subbasins present contrasts regarding magnetism and water depths, with slightly deeper water in the Southwest Subbasin.The marginal basin sediments are mostly of terrigenous origin, deposited during the Oligocene (~32 Ma), with high sedimentation rates in relation to the global average (~6.22 cm/ky) (Wang and Li, 2009).
We investigated the uppermost sediments retrieved from Holes U1431D, U1432C, and U1433A for foraminifer content.Hole U1431D (15°22′N, 117°00′E; 4240 m water depth), Hole U1432C (18°21.0831′N,116°23.4504′E;3829 m water depth), and Hole U1433A (12°55.1380′N,115°2.8345′E;4379 m water depth) were retrieved from the SCS central East, northern East, and Southwest Subbasins, respectively (Figure F1), during Expedition 349 onboard the R/V JOIDES Resolution (see the Expedition 349 summary chapter [Li et al., 2015]).The uppermost sediments of Hole U1431D (0-21.46mbsf ) are composed of dark greenish gray clay and silty clay with minor clayey silt, with variable amounts of nannofossil ooze and volcanic ash.The uppermost Hole U1432C sediments (0-24.23 mbsf ) are composed of dark greenish gray clay and clay with silt.Hole U1433A (0-244.15mbsf ) sediments are composed of dark greenish gray clay with rare interbeds of thin and very thin (<5 mm) clayey silt.In the upper parts of the hole, dark brownish clay layers intercalate with minor light greenish gray clay with nannofossils and nannofossil ooze layers.
Based on shipboard biostratigraphy analysis, the uppermost sediments of Holes U1431D and U1432C encompass the middle to late Pleistocene, and Hole U1433A encompasses the late Pleistocene.Sedimentation rates based on biostratigraphy and magnetostratigraphy are ~5, 12, and 20 cm/ky for Holes U1431D, U1432C, and U1433A, respectively (see the Expedition 349 summary chapter [Li et al., 2015]).

Material and methods
For this study, ~10 cm 3 samples (N = 132) were collected at a sampling resolution of 20 cm over the uppermost sections of Holes U1431D, U1432C, and U1433A.Samples were freeze-dried and are archived in the Paleoceanography and Paleoclimatology Laboratory (LabPaleo2) at the Center for Marine Studies (Federal University of Paraná-UFPR, Pontal do Paraná, Brazil).Samples from Holes U1431D (N = 44), U1432C (N = 43), and U1433A (N = 22) were selected for quantitative planktonic foraminiferal analysis.Each sample was weighed and shaken with distilled water for ~2 h for sediment disaggregation.Samples were then washed with water through a 63 μm mesh sieve and oven-dried at 40°C.To estimate planktonic foraminifer total abundance (tests/g of dry sediment), at least 300 specimens from the >150 μm size fraction were picked under a stereomicroscope and stored on slides.

Results
Planktonic foraminifer abundances for Holes U1431D, U1432C, and U1433A are shown in Table T1 and illustrated in Figure F2.

N
Table T1.Planktonic foraminifer (PF) abundances, Holes U1431D, U1432C, and U1433A.Download table in CSV format.Hole U1432C, the site with the shallowest water depth, yields the highest planktonic foraminifer abundances, varying from 1 to 904 tests/g of dry sediment.Lower planktonic foraminifer abundances are observed in Hole U1431D, with abundances ranging from 0 to 251 tests/g of dry sediment.Hole U1433A samples, from the deepest of the three sites, are barren of planktonic foraminifers in the >150 μm size fraction.
Planktonic foraminifer abundance changes and variations in test preservation observed between Holes U1431D and U1432C high-light the need for future studies regarding changes in SCS deepseawater chemistry.On the other hand, the absence of planktonic foraminifers in the mid-upper Pleistocene sequences of Hole U1433A preclude using this proxy for paleoceanographic studies due to poor carbonate preservation.