> The researchers used geochemical and ecological data from ocean sediments to reconstruct the change in water column properties over the past 800 years. They p

> The researchers used geochemical and ecological data from ocean sediments to reconstruct the change in water column properties over the past 800 years. They precisely dated sediments using a combination of methods and looked for diagnostic signs of Atlantification, like change in temperature and salinity. Then, from the original paper: > Here, we use lipid-based water temperature proxies (UK37 U 37 K and TEXL86 TEX 86 L ) and benthic foraminiferal data (distribution and δ18O) to reconstruct changes in water mass properties. Specifically, we examined anomalies in our proxy records to identify diagnostic signs of Atlantification. On the basis of a precise chronology, we combine our results with other local climate records to provide an integrated understanding of Atlantification and resolve its timing. Last, our reconstructions are compared with records of ocean and atmosphere circulation patterns to investigate the connections between the high Arctic and North Atlantic dynamics. https://www.science.org/doi/10.1126/sciadv.abj2946 https://www.science.org/doi/10.1126/sciadv.abj2946 Lipid-based water temperature proxies use the distribution of lipids deposited by organisms in sediment to deduce temperature. And... > Benthic foraminifera are single-celled organisms similar to amoeboid organisms in cell structure. https://pubs.usgs.gov/pdf/of/of99-45/foram.pdf https://pubs.usgs.gov/pdf/of/of99-45/foram.pdf So the technique appears to be based on isotopic and lipid analysis of sediments deposited by certain organisms. If you can date the sediments and are confident in the link between analyte concentration and temperature, and correct for various factors, you can reconstruct a time/temperature plot.