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The response of the hydrological cycle to anthropogenic climate change, especially across the tropical oceans, remains poorly understood due to the scarcity of long instrumental temperature and hydrological records. Massive shallow-water corals are ideally suited to reconstructing past oceanic variability as they are widely distributed across the tropics, rapidly deposit calcium carbonate skeletons that continuously record ambient environmental conditions, and can be sampled at monthly to annual resolution. Climate reconstructions based on corals primarily use the stable oxygen isotope composition (δ18 O), which acts as a proxy for sea surface temperature (SST), and the oxygen isotope composition of seawater (δ18 O sw), a measure of hydrological variability. Increasingly, coral δ18 O time series are paired with time series of strontium-to-calcium ratios (Sr/Ca), a proxy for SST, from the same coral to quantify temperature and δ18 O sw variability through time. To increase the utility of such reconstructions, we present the CoralHydro2k database, a compilation of published, peer-reviewed coral Sr/Ca and δ18 O records from the Common Era (CE). The database contains 54 paired Sr/Ca – δ18 O records and 125 unpaired Sr/Ca or δ18 O records, with 88 % of these records providing data coverage from 1800 CE to the present. A quality-controlled set of metadata with standardized vocabulary and units accompanies each record, informing the use of the database. The CoralHydro2k database tracks large-scale temperature and hydrological variability. As such, it is well-suited for investigations of past climate variability, comparisons with climate model simulations including isotope-enabled models, and application in paleodata-assimilation projects. The CoralHydro2k database is available in Linked Paleo Data (LiPD) format with serializations in MATLAB, R, and Python and can be downloaded from the NOAA National Center for Environmental Information's Paleoclimate Data Archive at 10.25921/yp94-v135 (Walter et al., 2022). [ABSTRACT FROM AUTHOR]

The tropical Pacific influences climate patterns across the globe, yet robust constraints on decadal to centennial‐scale climate variations are difficult to extract from sparse instrumental observations in this region. Oxygen isotope (δ18O) records from long‐lived corals enable the quantitative reconstruction of tropical Pacific climate variability and trends over the twentieth century and beyond, but such corals are exceedingly rare. Here, we use multiple short coral δ18O records to create a coral 'ensemble' reconstruction of twentieth century climate in the central tropical Pacific. Ten U/Th‐dated fossil coral δ18O records from Kiritimati Island (2°N, 157°W) span 1891 CE to 2006 CE, with the younger samples enabling quantitative comparison to a large ensemble of modern coral records and instrumental sea surface temperature. A composite record constructed of modern and fossil Kiritimati coral δ18O records shows a shift toward warmer and fresher conditions from 1970 CE onward, consistent with previously published records in this region. Plain Language Summary: The tropical Pacific plays a major role in shaping global temperature and rainfall patterns, but sparse instrumental observations prior to ∼1950 CE hamper the detection of potential anthropogenic climate signals against the rich background of natural variability in this region. This study demonstrates the utility of reconstructing twentieth century climate trends using an ensemble of multiple, short coral records in data‐sparse regions of the tropics. When applied to the central equatorial Pacific, coral data from Kiritimati Atoll resolve a twentieth century shift toward warmer and wetter conditions in this region, in line with evidence from continuous, century‐long coral records previously published from this region. Key Points: Ensembles of short fossil coral δ18O records yield robust estimates of nineteenth‐twentieth century climate variability and trendsSeawater δ18O contributions to Kiritimati coral δ18O are larger on multi‐decadal timescales than on interannual timescalesCoral δ18O records reveal a trend toward warmer and wetter conditions in the central equatorial Pacific over the twentieth century [ABSTRACT FROM AUTHOR]