DOI: 10.6071/m3q090
title: Data from: Ecological and environmental stability in offshore Southern California Marine Basins through the Holocene

description: In the face of ongoing marine deoxygenation, understanding timescales and
 drivers of past oxygenation change is of critical importance. Marine
 sediment cores from tiered silled basins provide a natural laboratory to
 constrain timing and implications of oxygenation changes across multiple
 depths. Here, we reconstruct oxygenation and environmental change over
 time using benthic foraminiferal assemblages from sediment cores from
 three basins across the Southern California Borderlands: Tanner Basin
 (EW9504-09PC, 1194 m water depth), San Nicolas Basin (EW9504-08PC, 1442
 m), and San Clemente Basin (EW9504-05PC ,1818 m). We utilize indicator
 taxa, community ecology, and an oxygenation transfer function to
 reconstruct past oxygenation, and directly compare reconstructed dissolved
 oxygen to modern measured dissolved oxygen. We generate new, higher
 resolution carbon and oxygen isotope records from planktic (Globigerina
 bulloides) and benthic foraminifera (Cibicides mckannai) from Tanner
 Basin. Geochemical and assemblage data indicate limited ecological and
 environmental change though time in each basin across the intervals
 studied. Early to mid-Holocene (11.0-4.7 ka) oxygenation below 1400 m (San
 Clemente and San Nicolas Basins) was relatively stable and reduced
 relative to modern. San Nicolas Basin experienced a multi-centennial
 oxygenation episode from 4.7-4.3 ka and oxygenation increased in Tanner
 Basin gradually from 1.7-0.8 ka. Yet across all three depths and time
 intervals studied, dissolved oxygen is consistently within a range of
 intermediate hypoxia (0.5-2.0 ml L-1 O2). Variance in reconstructed
 dissolved oxygen was similar to decadal variance in modern dissolved
 oxygen and reduced relative to Holocene-scale changes in shallower basins.
description: Full description of data is available in forthcoming
 publication. We investigate three piston cores
 collected from the Southern California Borderlands on the Maurice Ewing
 Cruise 9504 in May - June 1995: EW 9504-09PC from Tanner Basin at 1194 m
 water depth, EW 9504-08PC from San Nicolas Basin at 1442 m water depth,
 and EW 9504-05 from San Clemente Basin at 1818 m water depth. All cores
 have 10.16 cm inner diameter. Cores were split on board the ship and were
 sampled at 2 cm intervals. All sample intervals used in this had an
 initial volume of 162.15 cm<sup>3</sup>. Sediments from the
 working half of the core were disaggregated in sodium hexametaphosphate
 washed over a 63 µm sieve (see Stott et al. 2000). Sediments were dried
 and stored in glass vials at the University of Southern California until
 they were processed for this study. EW 9504-09PC (Tanner Basin) was
 examined from 0-40 cm at 2 cm intervals; intervals below 40 cm were not
 available for analysis. EW 9504-08PC (San Nicolas Basin) was examined at 2
 cm intervals from 0-22 cm and every 6 cm from 24-64 cm. EW 9504-05 (San
 Clemente Basin) was examined at 2 cm intervals from 30-52 cm; intervals
 from 0-30 cm in EW9504-05 did not have sufficient foraminifera for robust
 analysis and were thus excluded from analysis.
 Radiocarbon based age models were developed for each core using a
 combination of previously published and newly generated planktic
 radiocarbon ages (Table S1, Figure S1). Five age dates within the Holocene
 (1 San Clemente, 1 Tanner, 2 San Nicolas) were previously measured (Stott
 et al., 2000). These AMS <sup>14</sup>C ages were completed
 using bulk planktonic foraminifera (weight ~3-5 mg) analyzed at the
 Lawrence Livermore National Laboratory (Stott et al., 2000). Three
 additional radiocarbon dates (1 San Clemente, 2 Tanner, 1 San Nicolas)
 from bulk planktic foraminifera were analyzed in this study. All samples
 for radiocarbon analysis were prepared by picking shell material from the
 &gt;150 µm fraction, rinsing shells in methanol, sonicating in
 methanol for 5-10 seconds, and rinsing twice with deionized water. Shells
 were then dried in a 60<sup>O</sup>C drying oven. Radiocarbon
 analysis was completed at the Lawrence Livermore National Laboratory using
 δ<sup>13</sup>C assumed values following the convention of
 Stuiver and Polach (1977). The reported age is given in radiocarbon years
 using the Libby half-life of 5568 years. Accelerator mass spectrometry
 ages were converted to calendar ages before present (BP) by calibration
 against the Marine20 curve using the open-source software “R” package
 Bchron (Haslett & Parnell, 2008; Heaton et al., 2020). Calibration
 included correction for reservoir ages for the Southern California Coast
 of 220.0 +/- 40.0 years (Ingram & Southon, 1996; Stuiver &
 Polach, 1977). Age/depth models for each core were generated using the
 Bayesian age-depth modeling functionality of Bchron.
 Stable isotope analyses from planktic and benthic foraminifera
 from EW9504-09 (Tanner Basin) were conducted on <em>Globigerina
 bulloides</em> planktic foraminifera and
 <em>Cibicides</em> <em>mckannai </em>benthic
 foraminifera from 0-40 cm at 2 cm intervals. Samples were prepared by
 picking from the &gt;150 µm size fraction (2-5 individual <em>C.
 mckannai</em> per interval, 15-25 <em>G. bulloides</em>
 per interval), rinsing in methanol, sonicating in methanol for 5-10
 seconds, and rinsing twice with deionized water. Planktic foraminifera
 were analyzed for δ<sup>18</sup>O and
 δ<sup>13</sup>C at the UC Davis Stable Isotope Laboratory and
 benthic foraminifera were analyzed at the UC Santa Cruz Stable Isotope
 Laboratory. Planktic carbon and oxygen isotope samples
 were analyzed using a GasBench II system interfaced with a Delta V Plus
 Isotope Ratio Mass Spectrometer at the UC Davis Stable Isotope Laboratory
 using standard UCD-SM92 (-1.94 for δ<sup>18</sup>O and 2.08‰
 δ<sup>13</sup>C) (Ostermann 2000). Values for
 δ<sup>13</sup>C and δ<sup>18</sup>O are expressed
 in per mil (‰) relative to Vienna Pee Dee Belemnite, and values are
 corrected for changes in linearity and instrumental drift. Benthic carbon
 and oxygen isotope samples were analyzed at the UC Santa Cruz Stable
 Isotope Laboratory by acid digestion using an individual vial acid drop
 Themo Scientific Kiel IV carbonate device interfaced to Thermo Scientific
 MAT 253 dual-inlet isotope ratio mass spectrometer. All samples were
 measured with several replicates of the externally calibrated Carrera
 Marble in-house standard reference material 'CM12' and the
 NBS-18 limestone international standard reference material. Values for
 δ<sup>13</sup>C and δ<sup>18</sup>O are expressed
 in per mil (‰) relative to Vienna Pee Dee Belemnite, and values are
 corrected for changes in linearity and instrumental drift. Data were
 combined with previously published records of planktic oxygen isotopes and
 benthic oxygen and carbon isotopes from the same core examined here
 (EW9504-09) to increase replicates in the late Holocene and to extend the
 record through the entire Holocene (Stott et al., 2000). As such, isotope
 records reflect analyses from three different laboratories.
 Samples were dry sieved over a 150 µm sieve and picked for
 benthic foraminiferal microfossils. Individual foraminifera were picked
 and identified from each interval to obtain &gt;100 individuals per
 sample. Morphometrics of benthic foraminifera,
 including length, width, and surface area were measured using ImageJ
 software. Length and width of each individual was measured to the longest
 and widest margins of the shell. Ostracods (Arthropoda
 - Ostracoda) and urchin spines (Echinodermata) were picked from the 150 µm
 sediment fraction at all intervals examined.
description: Here, benthic foraminiferal assemblages are reported in raw
 values. All data in accompanying manuscript is discussed in relative
 abundance by dividing the number of individuals of a single species by the
 total number of foraminifera identified in that interval.
 Radiocarbon ages, table isotope records, invertebrate assemblage,
 and morphometrics all follow standard conventions and should be readable
 as presented.