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Results | |
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Preliminary results of first manuscript | |
| 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. |
Figure explanation: The different rows of this plot correspond to changes in different community metrics (1. richness, 2. gains, 3. losses) calculated for each individual site. The first column shows the data as density plots and the second column shows the same data as box plots separated by the specific plankton groups. The third column shows the change of the specific community metric in a geographical context. | Overview of site-specific community metrics of North Atlantic Ocean data set 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) calculated for each sample at each site. The site-specific change is then calculated as the slope of the linear model. Gains/losses change: For each sample, I calculated the species 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 (I always compared it to the oldest sample in the data setrecord). 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. |
| Gridded Hovmoller plots for richness [# and %], Shannon and Inverse Simpson diversity expressed as residuals from LGM mean
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| LDG plots (binned by age) for richness [# and %], Shannon and Inverse Simpson diversity expressed as residuals from LGM mean (loess smooth)
→ Progressive changes through time and space during the deglaciation and continuing into the Holocene? |
| Hovmoller plot: gridded Bray-Curtis distance to oldest tropical sample
→ Indication of tropical species moving into mid latitudes during the last deglaciation?
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Presentations | |
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Publications | |
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