Reconstructing past thermal conditions in beach microclimates

Abstract

Reconstruction of past conditions provides important information on how ecosystems have been impacted by climate change, but generally for microhabitats worldwide there are no long-term empirical measurements. In these cases, there has been protracted debate about how various large-scale environmental proxies can best be used to reconstruct local temperatures. Here we help resolve this debate by examining how well environmental proxies hindcast sand temperatures at nest depths for five sea turtle nesting sites across the world. We link instrumental air temperature and sea surface temperature records with empirical sand temperature observations in the Atlantic (Ascension Island and Cape Verde), the Indian Ocean (Chagos Archipelago), the Caribbean (St Eustatius) and the Pacific (French Polynesia). We found strong correlations between sea surface temperatures, air temperatures and sand temperatures at all our study sites. Furthermore, Granger causality testing shows variations in sea surface temperature and air temperature precede variations in sand temperatures.We found that different proxies (air or sea temperature or a combination of both) predicted mean monthly sand temperatures within <0.5°C of empirical observations. Reconstructions of sand temperatures over the last 170 years reveal a slight warming of temperatures (maximum 0.5°C per century). An analysis of 36 published datasets revealed that the gradient of the relationship between sand temperature and air temperature is relatively constant, suggesting long-term changes in sand temperature could be extended around the world to include nesting sites where there are no empirical measurements of sand temperature. Our approaches are likely to have utility for a range of microhabitats where there is an interest in long-term changes in temperature.

Short‐term resilience to climate‐induced temperature increases for equatorial sea turtle populations

“…In corroboration with previous studies (e.g. Fuentes et al, 2009; Laloë et al, 2021), we showed that AT is strongly correlated with sand temperatures at the nest depth on sea turtle nesting beaches. There are likely several reasons for the residual variation on plots of sand temperature explained by environmental proxies.…”

Can a present-day thermal niche be preserved in a warming climate by a shift in phenology? A case study with sea turtles

“…Previous work has shown that SST and air temperature (AT) measured over large scales near nesting sites are tightly correlated with sand temperature at nest depths [ 48 – 51 ]. More recently it was shown that the gradients of these relationships are consistent across sites, and that for every 1°C increase in AT, sand temperature at nest depth increases by an average 0.86°C (standard deviation = 0.26°C, n = 36; [ 52 ]). Similarly, for every 1°C increase in SST, sand temperature increases by an average 0.72–0.83°C [ 48 , 52 ].…”

“…More recently it was shown that the gradients of these relationships are consistent across sites, and that for every 1°C increase in AT, sand temperature at nest depth increases by an average 0.86°C (standard deviation = 0.26°C, n = 36; [ 52 ]). Similarly, for every 1°C increase in SST, sand temperature increases by an average 0.72–0.83°C [ 48 , 52 ]. In other words, because of the tight positive relationship between SST and sand temperature it is very likely that if SST rises at one site, so will sand temperature at nest depth.…”

Climate warming and sea turtle sex ratios across the globe

“…Previous studies from nesting sites across the world have shown that air temperatures in the 4° by 4° quadrats reflect sand temperatures at nest depth at nesting sites (e.g. Esteban et al, 2016;Hays et al, 2003) and typically a 1°C increase in air temperature equates to a 0.86°C increase in sand temperature at nest depth (Laloë, Chivers, et al, 2021). We obtained air temperatures for 1° by 1° boxes and calculated a mean monthly air temperature for each 4° by 4° quadrat weighing values by the number of observations in each 1° by 1° quadrat.…”

“…Air temperatures have repeatedly been shown to be closely linked to sand temperatures at sea turtle nest depth, including studies at nesting beaches in Ascension Island (South Atlantic; Hays et al, 2003), the Chagos Archipelago (Indian Ocean; Laloë, Chivers, et al, 2021), in Florida (West Atlantic; Hawkes et al, 2007) and around Australia (South Pacific; Fuentes et al, 2009Fuentes et al, , 2010. Predictions of sand temperatures from sand versus air temperature models have been shown to be close to measured sand temperatures (Laloë et al, 2017;Laloë, Chivers, et al, 2021) and so air temperature has been used many times as a proxy for predicting likely temporal changes in mean incubation temperatures at nest depths across decades (e.g. Fuentes et al, 2009Fuentes et al, , 2010Hawkes et al, 2007;Jensen et al, 2018;Laloë, Chivers, et al, 2021).…”