The potential of coralline algae as SST proxy and for climate model evaluation: A New Zealand case study

General circulation models (GCMs) are currently the most important tools for obtaining projections about future climate. In addition, they provide data input for regional atmospheric models that translate global climate change to regional and local scales where humans and environments face the impacts. To ensure the accurateness of their simulations, GCMs need to be evaluated as thoroughly as possible against past climate records, where one focus is on the so-called "historical period" (1850–present). However, the evaluation task is difficult for the period before World War II and earlier due to a frequent lack of reliable observations. This problem is exacerbated for the Southern Hemisphere, which has been notoriously understudied in comparison to the climate of the Northern Hemisphere.

In New Zealand, variations in sea surface temperature (SST) are reflected on a variety of spatial and temporal scales and are statistically detectable through to temperature anomalies and glacier mass balance changes in the high mountains of the Southern Alps. The correct simulation of SST by GCMs is therefore crucial, especially when investigating the physical mechanisms that transform large-scale SST signals into local climate anomalies by using regional atmospheric modeling.

In the project “NZ-PROXY”, we utilize crustose coralline algae (CCA) – a rather recently discovered proxy archive – to extend the observational time series of SST in the New Zealand region back to ~1850. The SST reconstruction is then employed in GCM evaluation to reveal their skill in representing the large-scale climate of New Zealand. Finally, high-resolution sensitivity simulations are obtained from a regional atmospheric model to investigate the added value of the advanced GCM selection for regional climate modeling.