Description: The Sr/Ca ratio of coral aragonite is used to reconstruct past sea surface temperature (SST). Twentyone laboratories took part in an interlaboratory study of coral Sr/Ca measurements. Results show interlaboratory bias can be significant, and in the extreme case could result in a range in SST estimates of 7°C. However, most of the data fall within a narrower range and the Porites coral reference material JCp- 1 is now characterized well enough to have a certified Sr/Ca value of 8.838 mmol/mol with an expanded uncertainty of 0.089 mmol/mol following International Association of Geoanalysts (IAG) guidelines. This uncertainty, at the 95% confidence level, equates to 1.5°C for SST estimates using Porites, so is approaching fitness for purpose. The comparable median within laboratory error is 〈0.5°C. This difference in uncertainties illustrates the interlaboratory bias component that should be reduced through the use of reference materials like the JCp-1. There are many potential sources contributing to biases in comparative methods but traces of Sr in Ca standards and uncertainties in reference solution composition can account for half of the combined uncertainty. Consensus values that fulfil the requirements to be certified values were also obtained for Mg/Ca in JCp-1 and for Sr/Ca and Mg/Ca ratios in the JCt-1 giant clam reference material. Reference values with variable fitness for purpose have also been obtained for Li/Ca, B/Ca, Ba/Ca, and U/Ca in both reference materials. In future, studies reporting coral element/Ca data should also report the average value obtained for a reference material such as the JCp-1.

Description: Nitrate concentration and isotopic (δ15NNO3) data, ice density, and surface mass balance estimates from the ABN1314-103 ice core. This 103 m long core was drilled beginning on 07 January 2014 as one of three ice cores at Aurora Basin North, Antarctica (-71.17, 111.37, 2679 m.a.s.l), in the 2013-2014 field season. The age-depth model for ABN1314-103 was matched through ion profiles from an annually-resolved model (ALC01112018) originally developed for one of the other ABN cores through seasonal ion and water isotope cycles and constrained by volcanic horizons. Each 1 m segment of the core was weighed and measured for ice density calculations, and then sampled for nitrate at 0.33 m resolution. Nitrate concentrations were taken on melted ice aliquots with ion chromatography, while isotopic analysis was achieved through bacterial denitrification and MAT 253 mass spectrometry after concentrating with anionic resin. Using the density data and the age-depth model's dates for the top and bottom of each 1 m core segment, we reconstructed a history of surface mass balance changes as recorded in ABN1314-103. Additionally, we also estimated the effect of upstream topographic changes on the ice core's surface mass balance record through a ground penetrating radar transect that extended 11.5 km against the direction of glacial ice flow. The modern SMB changes along this upstream transect were linked to ABN1314-103 core depths by through the local horizontal ice flow rate (16.2 m a-1) and the core's age-depth model, and included here for comparative analysis. See Akers et al., 2022 for more analytical details.

Description: Nitrate samples were originally collected as 0.2-1.5 kg snow samples in the field along the CHICTABA traverse, Antarctica. Snow was collected in three methods: snow pits, skin layer, and 1 m depth layer. For snow pits, snow was collected in increments of 3 cm thick layers. Skin layer samples were collected as the loose snow grains 2-6 mm deep on the surface. The 1 m depth layer samples were taken as a 5-10 cm thick layer surrounding 1 m depth, which was then thoroughly mixed. Samples were melted and nitrate concentrated with a ion exchange resin at Concordia Station, Antarctica. Isotopic analysis performed with MAT253 mass spectrometer at IGE, Grenoble, France.

Description: he last glacial was punctuated by several massive ice sheet surges into the North Atlantic that impacted surface water hydrology especially where icebergs melted. However, the links between variations in surface water hydrology and surface water productivity during these Heinrich events (HEs) remain uncertain. To address this issue, diatoms and organic carbon were examined across Heinrich event 1 (HE 1) and Heinrich event 4 (HE 4) in seven sediment cores spanning 40°N to 63°N latitude. Our results show low diatom abundances during HEs, consistent with decreased surface water productivity. Diatom dilution by increased sediment flux was tested by normalizing diatom abundance to a constant 230Th flux. Although the particle rain rate was enhanced during HEs, this does not explain the sharp drop in diatoms. During HE 4, surface productivity decreased at all latitudes examined, probably because of strong, year-round stratification. The same inferred changes occurred during HE 1 within the area of maximum iceberg melting. However, at northern latitudes (above 50°N) the summer insolation increase of the glacial termination drove increased surface productivity during the whole period, including HE 1. Marine organic carbon, taken as independent proxy for export production, supports the diatom data. Trends shown by the productivity proxies evolve generally in parallel with the hydrographic proxies, with an increase in productivity when sea surface temperature increases.

Description: This dataset contains isotopic ratios of nitrate analyzed from snow samples collected along the CHICTABA traverse in East Antarctica in Nov 2013-Jan 2014. Supplemental information on the elevation (doi:10.5194/tc-13-665-2019) and surface mass balance changes (doi:10.5194/tc-13-281-2019) along the traverse route are also included for context. The samples came from relatively shallow depths of the snowpack (maximum = 2.03 m deep) and represent nitrate deposition that occurred from 0-6 years ago. These samples were collected in order to better understand the interaction and mass transfer of nitrate at the snow-air interface in Antarctica, with particular focus on determining the impacts of photolysis on nitrate. Snow samples were collected with three techniques: skin layer samples of the loose snow grains 2-6 mm deep on the snow surface, 1 m depth layer samples taken as a 5-10 cm thick layer from 1 m below the snow surface, and snow pits that extended 99-203 cm deep and were sampled at 3 cm continuous intervals. 250-1500 g of snow were collected into clean plastic bags, melted at room temperature at Concordia Station, Dome C, and then the nitrate was concentrated using an ionic exchange resin. Nitrate concentrations were determined using colorimetry. Isotopic analysis occurred at the Institut des Géosciences de l'Environnement, Grenoble, France, through bacterial denitrification and a MAT 253 mass spectrometer with Gas Bench.

Description: We generated a high-resolution SSTMg/Ca record for the surface-dwelling planktonic foraminifera Globigerina bulloides from the core MD99-2346 collected in the Gulf of Lion, and compared it to that obtained using modern analogue techniques applied to fossil foraminiferal assemblages (SSTMAT). The two temperature records display similar patterns during the last 28,000 years but the SSTMg/Ca estimates are several degrees warmer (~+4 °C) than SSTMAT. The temperature shift between SSTMg/Ca and SSTMAT remained relatively constant over time. This seems to exclude a bias on the Mg/Ca record associated with salinity or secondary Mg-rich calcite encrustation on the foraminiferal tests during early diagenesis. Therefore, anomalously high Mg/Ca suggests either: (1) the empirical equation for G. bulloides of Elderfield and Ganssen (2000) is incorrect; or (2) there is a specific Mediterranean genotypes of G. bulloides for which a specific Mg/Ca-temperature calibration is needed.