Data from: Oxygenation of offshore Southern California marine basins through the Holocene
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. Her...
| Main Authors: | , , , , , , |
|---|---|
| Format: | Dataset |
| Language: | English |
| Published: |
Dryad
2021
|
| Subjects: | |
| Online Access: | https://dx.doi.org/10.6071/m3q090 http://datadryad.org/stash/dataset/doi:10.6071/M3Q090 |
| Summary: | 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 change over time using benthic foraminiferal assemblages from three sediment cores, EW9504-09PC (Tanner Basin, 1194 m water depth), EW9504-08PC (San Nicolas Basin, 1442 m), and EW9504-05PC (San Clemente Basin, 1818 m) across the Southern California Borderlands. 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. Early to mid-Holocene (11.2-4.7 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 4.7-4.2 ka and oxygenation increased in Tanner Basin gradually from 5.5-1.9 ka. Oxygenation of these offshore basins is synchronous with an increase in oxygenation in Santa Barbara Basin at ~6 ka and may be due to increased oxygenation of North Pacific Intermediate Water. Yet across all three depths and time intervals studied, dissolved oxygen is consistently within a range of intermediate hypoxia (0.5-1.5 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. : 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 cm3. 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. Five age dates within the Holocene (1 San Clemente, 1 Tanner, 2 San Nicolas) were previously measured (See Stott et al., 2000). These AMS 14C ages were completed using bulk planktonic foraminifera (weight ~3-5 mg) analyzed at the Lawrence Livermore National Laboratory (See 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 >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 60OC drying oven. Radiocarbon analysis was completed at the Lawrence Livermore National Laboratory using δ13C 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. The Calib7.1 calibration program was used to calibrate ages using a reservoir age of 220.0 +/- 40.0 (Ingram & Southon, 1996; Stuiver & Polach, 1977). The age model for each core was generated using liner interpolation between radiocarbon age dates. Stable isotope analyses from planktic and benthic foraminifera from EW9504-09 (Tanner Basin) were conducted on Globigerina bulloides planktic foraminifera and Cibicides mckannai benthic foraminifera from 0-40 cm at 2 cm intervals. Samples were prepared by picking from the >150 µm size fraction (2-5 individual C. mckannai per interval, 15-25 G. bulloides per interval), rinsing in methanol, sonicating in methanol for 5-10 seconds, and rinsing twice with deionized water. Planktic foraminifera were analyzed for δ18O and δ13C 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 δ18O and 2.08‰ δ13C) (Ostermann 2000). Values for δ13C and δ18O 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 δ13C and δ18O 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 >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. : 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. |
|---|