Description: Modern and archaeological catfish otoliths (Carlarius spp.) and bivalve shells (Senilia senilis) from a large paleo-estuary east of the Banc d'Arguin, Mauritania, NW Africa, were assessed to obtain information on paleoenvironmental conditions and the NW African hydroclimate during the mid- to late Holocene (ca. 3.0 - 5.3 ka BP). High-resolution (sub-seasonally resolved) ontogenetic stable oxygen isotope (δ18O) records and bulk 87Sr/86Sr analyses indicate monsoonal discharge to the Banc d'Arguin between 5.0 to 5.3 ka BP. Carbonate clumped isotope thermometry was used to test archaeological samples for potential pre-depositional alteration due to prehistoric cooking treatments.

Description: In the South Pacific Convergence Zone (SPCZ), the variability in a sub-seasonally resolved microatoll Porites colony Sr/Ca record from Tonga and a previously published high-resolution record from Fiji are strongly influenced by sea surface temperature (SST) over the calibration period from 1981 to 2004 (R^2 = 0.67 - 0.68). However, the Sr/Ca-derived SST correlation to instrumental SST decreases back in time. The lower frequency secular trend (~1°C) and decadal-scale (~2 - 3°C) modes in Sr/Ca-derived SST are almost two times larger than that observed in instrumental SST. The coral Sr/Ca records suggest that local effects on SST generate larger amplitude variability than gridded SST products indicate. Reconstructed d18O of seawater (d18Osw) at these sites correlate with instrumental sea surface salinity (SSS; r = 0.64 - 0.67) but not local precipitation (r = -0.10 to - 0.22) demonstrating that the advection and mixing of different salinity water masses may be the predominant control on d18Osw in this region. The Sr/Ca records indicate SST warming over the last 100 years and appears to be related to the expansion of the western Pacific warm pool (WPWP) including an increasing rate of expansion in the last ~20 years. The reconstructed d18Osw over the last 100 years also shows surface water freshening across the SPCZ. The warming and freshening of the surface ocean in our study area suggests that the SPCZ has been shifting (expanding) southeast, possibly related to the southward shift and intensification of the South Pacific gyre over the last 50 years in response to strengthened westerly winds.

Description: Increasing atmospheric CO2 from man-made climate change is reducing surface ocean pH. Due to limited instrumental measurements and historical pH records in the world's oceans, seawater pH variability at the decadal and centennial scale remains largely unknown and requires documentation. Here we present evidence of striking secular trends of decreasing pH since the late nineteenth century with pronounced interannual to decadal–interdecadal pH variability in the South Pacific Ocean from 1689 to 2011 CE. High-amplitude oceanic pH changes, likely related to atmospheric CO2 uptake and seawater dissolved inorganic carbon fluctuations, reveal a coupled relationship to sea surface temperature variations and highlight the marked influence of El Niño/Southern Oscillation and Interdecadal Pacific Oscillation. We suggest changing surface winds strength and zonal advection processes as the main drivers responsible for regional pH variability up to 1881 CE, followed by the prominent role of anthropogenic CO2 in accelerating the process of ocean acidification.

Description: Sub-seasonally resolved and replicated coral Sr/Ca time series at Clipperton Atoll (10°18'N, 109°13'W) in the eastern Pacific are assessed as a sea surface temperature (SST) proxy in this region with small seasonal SST variability. The composite coral Sr/Ca time series is a partially replicated record of three live and one sub-modern colony of Porites lobata extending back to 1874. Large inter-colony coral Sr/Ca offsets equate to relative SST differences of 0.6 to 4.3 °C and limit the ability to reconstruct absolute SST changes. Moreover, the replication method revealed a 12-year section of growth in one colony where mean Sr/Ca was anomalously low (~ 1 °C higher SST) relative to the other colonies without evidence of diagenesis or other significant skeletal alterations. The presence of this anomalous interval supports the need for multi-coral Sr/Ca replication in specific sites or regions. The Clipperton Composite Sr/Ca anomaly record is significantly coherent (r = 0.71-0.76, p 〈 0.001) with gridded instrumental SSTs but with larger amplitude decadal variance that appears to more accurately represent actual SST variability at Clipperton. The amplitude of the secular warming trend during the last century at Clipperton is 0.3 to 0.6 °C larger (~ twice as large) than the trend in the poorly "ground-truthed" instrumental SST records for the region. The interannual and decadal variability in Clipperton coral Sr/Ca demonstrates strong coherence to the Pacific Decadal Oscillation and the El Niño/Southern Oscillation (ENSO) with reduced ENSO variability from 1920 to late 1930s and enhanced variability in the late twentieth century.

Description: Massive corals act as a climate archive for the tropical oceans. They can provide valuable information in regions that have no or limited observations such as the southern Gulf of Mexico (GOM), where there is almost no information reaching back to preindustrial times on sea surface temperature (SST) or sea surface salinity (SSS) available. For the reconstruction of SST and SSS in the southern GOM the massive coral Siderastrea siderea was cored in 2005 providing a time window into the past reaching from 1845 to 2005 CE. The coral core was cut and X-rayed and bimothly samples were drilled with a Proxxon drill and 0.4 mm diamant coated drill bit. Oxygen isotopes were measured at the MARUM facilities in Bremen with a Finnigan MAT 251 and Finningan Mat 253plus isotope ratio mass spectrometer. Trace element analysis was done at the ZMT facilities in Bremen on a Plasma Quant MS Elite Inductively Coupled Plasma - Mass Spectrometer. The Dataset also includes reconstructed δ18OSW after data Ren et al. (2002) as well as the detrended δ18OSW dataset and Pseudo Coral model data (Thompson et al., 2011). The age model for the dataset was interpolated using the Arand software Ager and Timer (Howell et al., 2006). Outliers were identified with the detection method provided by Chen and Liu (1993).

Description: Modern sub-surface water samples and the otoliths of catfish (Carlarius parkii and Chrysichthys nigrodigitatus) collected from the estuaries of the Gambia River (The Gambia), Sine-Saloum (Senegal), and Volta River (Ghana) in 2017 were analysed to investigate relationships between the Sr geochemistry and salinity. 87Sr/86Sr, Sr concentration, and salinity measured in water samples collected along the estuarine salinity gradients were used to establish mixing models describing their relationships. Bulk catfish otolith 87Sr/86Sr measurements were used to estimate habitat salinity of the fish based on these mixing models. Catch data (total length, fork length, weight) of catfish were recorded and used to estimate their age. Fish ages were further estimated based on otolith annuli.

Description: Modern sub-surface water samples and the otoliths of catfish (Carlarius parkii and Chrysichthys nigrodigitatus) collected from the estuaries of the Gambia River (The Gambia), Sine-Saloum (Senegal), and Volta River (Ghana) in 2017 were analysed to investigate relationships between the Sr geochemistry and salinity. 87Sr/86Sr, Sr concentration, and salinity measured in water samples collected along the estuarine salinity gradients were used to establish mixing models describing their relationships. Bulk catfish otolith 87Sr/86Sr measurements were used to estimate habitat salinity of the fish based on these mixing models. Catch data (total length, fork length, weight) of catfish were recorded and used to estimate their age. Fish ages were further estimated based on otolith annuli.