We used the records of the planktonic foraminifera data set to first determine the shape of the major compositional change in each record by principle components analyses. The mean global response of the plankton to the deglaciation was then evaluated by an Empirical Orthogonal Function (EOF) analysis of the main biotic trends across all sites.

We find that the dominant response of the zooplankton consists of synchronous unidirectional shifts initiated between 16-17 ka BP, and progressing into the Holocene. When regressed on the global ocean temperature and CO₂ trends, we can see a proportionate response to the forcing during the last glacial maximum, the deglaciation and the early Holocene. In contrast, the late Holocene is characterised by continued compositional change, which does not appear related to environmental forcing. We speculate that this decoupling indicates the existence of a multi-millennial delay in community change following the climatic forcing.

We calculated changes in community metrics (richness, gains and losses) for each record of the North Atlantic Ocean data set for the last 24 ka. This overview plot shows consistent change in the flora/fauna such as increasing number of species at mid latitudes and decreasing number at low latitudes. Furthermore, the change in species gains is most prominent at mid latitudes whereas most species losses during the last deglaciation occur at low latitudes. This change could reflect species moving, but could also imply formation of new communities (i.e. with different composition than found anywhere).

Methods:

Richness change: Species richness (# of species) for each sample at each site. The site-specific change is then calculated as the slope of the linear model.

Gains/losses change: Species gains and losses (in percent) as the proportion of species either gained or lost relative to the total number of species observed across both time periods (always compared to the oldest sample in the record). Note: the species gains/losses take actual species identity into account, it’s not only the change in # of species. The site-specific change is then again calculated as the slope of the linear model.

NOTE: A negative slope (red colour in geographical maps) in e.g. richness change means that the number of species increased from the LGM to recent times. It’s kind of counter-intuitive, but it’s because of the x-axis (time). However, for a better intelligibility, this can be easily changed.