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  • 1
    Publication Date: 2023-06-21
    Description: Individual species were identified and 550 individuals per species were picked from the 〉250 µm fraction under dissecting microscope for each sample. Approximately 7 mg of picked and identified foraminifera shells were crushed between glass microscope slides and rinsed with MilliQ water. Samples were cleaned prior to δ¹⁵NFB measurement as described in Marcks et al., (2023). Once samples were clean, organic nitrogen was released into solution by acid dissolution of the foraminiferal calcite. Samples were acidified prior to measurement. Nitrate concentrations were measured by chemiluminescence on a Teledyne Instruments (Model 200E) chemiluminescence NO/NOx analyzer. δ15NFB samples, 10 nmol in size, were measured by bacterial conversion of nitrate to nitrous oxide, with measurement of the δ¹⁵N of the nitrous oxide by automated extraction and gas chromatography-isotope ratio mass spectrometry on a Thermo Delta V Plus IRMS. The potassium nitrate reference materials IAEA-N3 and USGS 34 (+4.7 ‰ and 1.8 ‰, respectively) were used to standardize results (Gonfiantini et al., 1995). Note, testing of a subset of 6 samples, each with full procedural triplicates, for a total of 18 samples, showed negligible differences in nitrogen content and δ¹⁵NFB values with and without a reductive cleaning step, and so it was omitted here to avoid unnecessary loss of sample material. Sample replicates and triplicates were analyzed when possible. Full procedural replicates were analyzed for 134 sample splits, representing 66 unique samples, when enough foraminifera were available for duplicate or triplicate analysis. The average standard deviation of procedural replicates is 0.4 ‰. Full operational blanks and amino acid standards (USGS 65 glycine) were measured in each batch. The average standard deviation of glycine standards measured in triplicate is 0.3 ‰. We estimated the δ¹⁵N value of the persulfate blank using a dilution series (5, 7.5, 10, and 20 μM of the glycine standard and the fraction of the blank in standards. We applied a blank correction to each sample based on the calculated mean δ¹⁵N value of all of the persulfate blanks for the dataset and the fraction of the blank in the N content of each sample. Data were subset to exclude N content outliers (〉2 s.d. from mean and where the blank was greater than 20 % of the sample N content, with significantly different δ¹⁵N values from other replicates). Full propagated analytical error associated with measurement and blank correction, following Higgins et al., (2009, doi:10.1021/ac8017185 ), was on average 0.6 ‰. Propagating the errors, including not only the procedural replicates and their variance, but the relative size of the blanks, the mean of the calculated blank δ¹⁵N values (5± 10 ‰). The mean value, 0.6 ‰, is used where procedural replicates were limited by sample availability. The age model is based on the benthic oxygen isotope stratigraphy presented by Starr et al. (2021, doi:10.1038/s41586-020-03094-7). This age model for Site 361-U1475 was generated with 12 radiocarbon dates and 33 benthic oxygen isotope tie points which were graphically aligned with a probabilistic stack of 180 globally distributed benthic oxygen isotope records (Starr et al., 2021, doi:10.1038/s41586-020-03094-7).
    Keywords: Agulhas Plateau; biogenic silica; Foraminifera-bound nitrogen isotopes; G. bulloides; G. inflata; mid-Pleistocene transition; N. pachyderma; opal; Subtropical Front
    Type: Dataset
    Format: application/zip, 3 datasets
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  • 2
    Publication Date: 2023-06-27
    Description: Individual species were identified and ~550 individuals per species were picked from the 〉250 µm fraction under dissecting microscope for each sample. Approximately 7 mg of picked and identified foraminifera shells were crushed between glass microscope slides and rinsed with MilliQ water. Samples were cleaned and prepared for δ¹⁵NFB measurement as in Smart et al. (2020, doi:10.1029/2019gc008440). Nitrate concentrations were measured by chemiluminescence on a Teledyne Instruments (Model 200E) chemiluminescence NO/NOx analyzer (Braman & Hendrix, 1989; doi:10.1021/ac00199a007). δ¹⁵NFB was measured by bacterial conversion of nitrate to nitrous oxide (Sigman et al., 2001; doi:10.1021/ac010088e), with measurement of the δ¹⁵N of the nitrous oxide by automated extraction and gas chromatography-isotope ratio mass spectrometry (Casciotti et al., 2002; doi:10.1021/ac020113w ) on a Thermo Delta V Plus IRMS. The potassium nitrate reference materials IAEA-N3 and USGS 34 (+4.7 ‰ and 1.8 ‰, respectively) were used to standardize results (Gonfiantini et al., 1995). Sample replicates and triplicates were analyzed when possible. Full procedural replicates were analyzed for 161 sample splits, representing 77 unique samples, when enough foraminifera were available for duplicate or triplicate analysis. Precision for full procedural replicates was 1.0 ‰, this is comparable with modern shell-bound measurements of the same species taken from net tows in this region (standard error = 0.9 ‰, n=10 & 1.1 ‰, n=6, of G. bulloides and G. inflata, respectively; Smart et al., 2020). In every batch, full operational blanks and amino acid standards (USGS 65 amino acid standard) were used to correct for the persulfate oxidation blank and to ensure complete conversion of N. The age model is based on the benthic oxygen isotope stratigraphy presented by Starr et al. (2021, doi:10.1038/s41586-020-03094-7).
    Keywords: 361-U1475B; 361-U1475E; 361-U1475F; AGE; Age model (Starr et al., 2021); Agulhas Plateau; biogenic silica; Chemiluminescence; DRILL; Drilling/drill rig; Event label; Exp361; Foraminifera-bound nitrogen isotopes; G. bulloides; G. inflata; Joides Resolution; Mass spectrometer Thermo Electron Delta plus IRMS; mid-Pleistocene transition; Nitrogen, total; opal; Sample code/label; Sample ID; South African Climates (Agulhas LGM Density Profile); Species; Species, unique identification (Semantic URI); Species, unique identification (URI); Subtropical Front; δ15N; δ15N, standard error
    Type: Dataset
    Format: text/tab-separated-values, 1453 data points
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  • 3
    Publication Date: 2023-06-27
    Description: Neogloboquadrina pachyderma abundance was obtained by washing ~ 10 cm³ of sediment through a 150µm sieve and drying at ~ 50 ºC for 24 h. This dried fraction was split until a total of 300-400 individuals remained. From this amount, we identified the relative abundance of Neogloboquadrina pachyderma tests according to Kennett and Srinivasan (1983) and Loeblich and Tappan (1988, doi:10.1007/978-1-4899-5760-3).
    Keywords: 361-U1475B; 361-U1475C; 361-U1475E; 361-U1475F; Abundance estimate; Age model; Age model (Starr et al., 2021); Agulhas Plateau; biogenic silica; Date/Time of event; DRILL; Drilling/drill rig; Event label; Exp361; Foraminifera-bound nitrogen isotopes; G. bulloides; G. inflata; Joides Resolution; Latitude of event; Longitude of event; mid-Pleistocene transition; Neogloboquadrina pachyderma sinistral; opal; Sample code/label; South African Climates (Agulhas LGM Density Profile); Subtropical Front
    Type: Dataset
    Format: text/tab-separated-values, 660 data points
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  • 4
    Publication Date: 2023-06-27
    Description: Biogenic silica accumulation was obtained by analyzing approximately 200 mg of homogenized and freeze dried sediment for each sample. Cleaning, chemical treatment, and measurement followed protocols outlined in (Mortlock & Froelich, 1989, doi:10.1016/0198-0149(89)90092-7). Samples were measured with a UV Vis spectrophotometer at 812 nm wavelength. Full procedural replicates were performed on 163 of the 435 samples yielding an average standard deviation of 0.2 %. Samples were referenced to RICCA VerSpec SiO32- in 1 % NaOH for intercomparison. Opal mass accumulation rates were calculated by multiplying the fraction of opal by dry bulk density and sedimentation rates from Starr et al. (2021, doi:10.1038/s41586-020-03094-7).
    Keywords: 361-U1475B; 361-U1475C; 361-U1475E; 361-U1475F; Accumulation rate, biogenic silica; Age model; Age model (Starr et al., 2021); Agulhas Plateau; biogenic silica; Calculated, see abstract; DRILL; Drilling/drill rig; Event label; Exp361; Foraminifera-bound nitrogen isotopes; G. bulloides; G. inflata; Joides Resolution; mid-Pleistocene transition; opal; Opal, biogenic silica; Sample code/label; South African Climates (Agulhas LGM Density Profile); Subtropical Front
    Type: Dataset
    Format: text/tab-separated-values, 1748 data points
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  • 5
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    PANGAEA
    In:  Supplement to: Povea, Patricia; Cacho, Isabel; Moreno, Ana; Pena, Leopoldo D; Menéndez, M; Calvo, Eva; Canals, Miquel; Robinson, Rebecca S; Mendez, Fernando J; Flores, José-Abel (2016): Atmosphere-ocean linkages in the eastern equatorial Pacific over the early Pleistocene. Paleoceanography, 31(5), 522-538, https://doi.org/10.1002/2015PA002883
    Publication Date: 2023-06-30
    Description: Here we present a new set of high-resolution early Pleistocene records from the eastern equatorial Pacific (EEP). Sediment composition from Ocean Drilling Program Sites 1240 and 1238 is used to reconstruct past changes in the atmosphere-ocean system. Particularly remarkable is the presence of laminated diatom oozes (LDOs) during glacial periods between 1.85 and 2.25 Ma coinciding with high fluxes of opal and total organic carbon. Relatively low lithic particles (coarse and poorly sorted) and iron fluxes during these glacial periods indicate that the increased diatom productivity did not result from dust-stimulated fertilization events. We argue that glacial fertilization occurred through the advection of nutrient-rich waters from the Southern Ocean. In contrast, glacial periods after 1.85 Ma are characterized by enhanced dust transport of finer lithic particles acting as a new source of nutrients in the EEP. The benthic ecosystem shows dissimilar responses to the high productivity recorded during glacial periods before and after 1.85 Ma, which suggests that the transport processes delivering organic matter to the deep sea also changed. Different depositional processes are interpreted to be the result of two distinct glacial positions of the Intertropical Convergence Zone (ITCZ). Before 1.85 Ma, the ITCZ was above the equator, with weak local winds and enhanced wet deposition of dust. After 1.85 Ma, the glacial ITCZ was displaced northward, thus bringing stronger winds and stimulating upwelling in the EEP. The glacial period at 1.65 Ma with the most intense LDOs supports a rapid southward migration of the ITCZ comparable to those glacial periods before 1.85 Ma.
    Keywords: Atmosphere; dust; Eastern Equatorial Pacific; ITCZ; ocean; ODP 1240; productivity
    Type: Dataset
    Format: application/zip, 16 datasets
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  • 6
    Publication Date: 2023-12-14
    Description: Intense seasonal productivity and carbon drawdown on the West Antarctic Peninsula (WAP) is driven by upwelling of nutrient-rich Circumpolar Deep Water (CDW) and subsequent stratification. CDW influence on the WAP is thought to have varied dramatically during the mid-Holocene, 5-7 ka. Here, we use diatom-bound nitrogen isotopes (δ15NDB), a nutrient utilization proxy, from ODP Site 1098 in Palmer Deep to study variations in the presence of CDW on sub-millennial timescales in the mid-Holocene. CDW intrusion is synchronous with atmospheric warming over Antarctica, suggesting that stronger and/or more southerly Southern Hemisphere westerlies enhanced CDW intrusion onto the WAP shelf. Our results also suggest that bulk sedimentary nitrogen isotopes (δ15Nbulk) do not track the same processes as δ15NDB at this site and that this cannot be explained by changes in diatom assemblages.
    Keywords: 178-1098B; AGE; Age model, Domack et al. (2001); Carbon; Carbon, organic, total; Carbon, organic, total, standard deviation; CDW; circumpolar deep water; Depth, composite; Diatom; diatoms; Drake Passage; DRILL; Drilling/drill rig; DSDP/ODP/IODP sample designation; Element analyser CHNSO, Costech ECS 4010; Joides Resolution; Leg178; Mass spectrometer Delta V; mid-holocene; nitrogen; Nitrogen, total; Nitrogen, total, standard deviation; nitrogen isotope ratios; nitrogen isotopes; Opal, biogenic silica; Opal, biogenic silica, standard deviation; paleoceanography; Sample code/label; sediment; Southern Ocean; Stratification; Upwelling; WAP; West Antarctic Peninsula; δ15N, bulk sediment; δ15N, bulk sediment, standard deviation; δ15N, diatom-bound organic matter; δ15N, diatom-bound organic matter, standard deviation
    Type: Dataset
    Format: text/tab-separated-values, 364 data points
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  • 7
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    PANGAEA
    In:  Supplement to: Robinson, Rebecca S; Meyers, Philip A; Murray, Richard W (2002): Geochemical evidence for variations in delivery and deposition of sediment in Pleistocene light-dark color cycles under the Benguela Current Upwelling System. Marine Geology, 180(1-4), 249-270, https://doi.org/10.1016/S0025-3227(01)00217-1
    Publication Date: 2024-01-09
    Description: Distinctive light-dark color cycles in sediment beneath the Benguela Current Upwelling System indicate repetitive alternations in sediment delivery and deposition. Geochemical proxies for paleoproductivity and for depositional conditions were employed to investigate the paleoceanographic processes involved in creating these cycles in three mid-Pleistocene intervals from ODP Sites 1082 and 1084. Concentrations of total organic carbon (TOC) vary between 3.5 and 17.1%. Concentrations of CaCO3 vary inversely to TOC and Al, which suggests that both carbonate dissolution and terrigenous dilution contribute to the light-dark cycles. Opal concentrations are independent of both TOC and CaCO3, therefore eliminating diatom production and lateral transport of shelf material as causes of the light-dark cycles. d13Corg and d15Ntot values do not vary across light-dark sediment intervals, implying that the extent of relative nutrient utilization did not change. The stable d15Ntot values represent a balanced change in nitrate supply and export production and therefore indicate that productivity was elevated during deposition of the TOC-rich layers. Parallel changes in concentrations of indicator trace elements and TOC imply that changes in organic matter delivery influenced geochemical processes on the seafloor by controlling consumption of pore water oxygen. Cu, Ni, and Zn are enriched in the darker sediment as a consequence of greater organic matter delivery. Redox-sensitive metals vary due to loss (Mn and Ba) or enrichment (Mo) under reducing conditions created by TOC oxidation. Organic matter delivery impacts subsequent geochemical changes such as carbonate dissolution, sulfate reduction and the concentration of metals. Thus, export production is considered ultimately responsible for the generation of the color cycles.
    Keywords: 175-1082A; 175-1084A; Benguela Current, South Atlantic Ocean; DRILL; Drilling/drill rig; Joides Resolution; Leg175; Ocean Drilling Program; ODP
    Type: Dataset
    Format: application/zip, 2 datasets
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  • 8
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    PANGAEA
    In:  Supplement to: Higgins, Meytal B; Robinson, Rebecca S; Carter, Susan J; Pearson, Ann (2010): Evidence from chlorin nitrogen isotopes for alternating nutrient regimes in the Eastern Mediterranean Sea. Earth and Planetary Science Letters, 290(1-2), 102-107, https://doi.org/10.1016/j.epsl.2009.12.009
    Publication Date: 2024-01-09
    Description: Nitrogen isotopes of chlorins, degradation products of chlorophyll, reflect the isotopic composition of nutrient N utilized by marine phytoplankton communities. Here we show that in sediments of the eastern Mediterranean Pleistocene and Holocene, values of d15N for chlorins and total nitrogen vary in concert, with a consistent offset of ~5 per mil reflecting the fractionation imparted during chlorophyll biosynthesis. Samples from the Integrated Ocean Drilling Program Sites 964 and 969 were analyzed at a sampling resolution of ~4-10 cm, clustered around sapropel events 2, 3, 4 and 5 (~100-170 ka). In low organic content sediments, chlorin values of ~0 per mil coincident with total nitrogen values of ~+ 5 per mil indicate that the latter reflects the original biomass and is not a consequence of diagenetic isotope enrichment. In sapropel horizons, the chlorin and total nitrogen values are 5 per mil more negative (~-5 per mil and ~ 0 per mil, respectively), resembling previously-reported, modern-day water-column particulates (~0 per mil). We suggest that nutrient conditions in the Eastern Mediterranean correspond to three scenarios and that the similarity between sapropel and modern-day bulk d15N is coincidental. Organic-poor marl sediments formed under oligotrophic conditions where surface productivity resulted from upwelling of Atlantic-sourced nitrate. Sapropels were characterized by enhanced diazotrophy that was likely fueled by increased riverine P fluxes to surface waters. Present-day conditions are dominated by anthropogenic N sources. These scenarios agree with a model of sapropel formation in which stratification caused by increased fresh-water inputs led to N fixation due to P:N nutrient imbalance. Enhanced production combined with stratification promoted and maintained anoxic deep waters, consequently increasing organic matter preservation. Such a model may be relevant to interpreting other episodes of intense organic matter deposition in past oceans.
    Keywords: 160-964; Carbon, organic, total; Carbon, organic, total, standard deviation; Comment; COMPCORE; Composite Core; DEPTH, sediment/rock; Eastern Basin; Joides Resolution; Leg160; Nitrogen, total; Nitrogen, total, standard deviation; Ocean Drilling Program; ODP; Sample comment; Δδ15N; Δδ15N, standard deviation; δ13C, organic carbon; δ13C, standard deviation; δ15N; δ15N, standard deviation
    Type: Dataset
    Format: text/tab-separated-values, 298 data points
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  • 9
    Publication Date: 2024-01-09
    Keywords: 202-1239; AGE; COMPCORE; Composite Core; Depth, composite; DEPTH, sediment/rock; Element analyser, Carlo Erba NC2500; Equatorial East Pacific; Intercore correlation; Joides Resolution; Leg202; Nitrogen, total; Ocean Drilling Program; ODP; δ15N, bulk sediment
    Type: Dataset
    Format: text/tab-separated-values, 1572 data points
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  • 10
    Publication Date: 2024-01-09
    Keywords: 202-1240; AGE; COMPCORE; Composite Core; Depth, composite; DEPTH, sediment/rock; Element analyser CHNSO, Costech ECS 4010; Equatorial East Pacific; Intercore correlation; Joides Resolution; Leg202; Nitrogen, total; Ocean Drilling Program; ODP; δ15N, bulk sediment
    Type: Dataset
    Format: text/tab-separated-values, 2106 data points
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