LAND-SEA CONNECTIVITY DURING A JURASSIC GLOBAL WARMING EVENT (Invited Presentation)

Terrestrial and marine ecosystems are both impacted by climate change, however, little is known on how climate change can affect land-sea ecological connectivity. Here we reconstruct the timing of degradation and recovery of land plants, marine primary producers and benthic macro-invertebrates over a period of 4 million years in response to a Jurassic global warming event (early Toarcian, around 180 Ma), and test for possible causal links between and within land and sea ecosystems using multiple regression analysis. Quantitative abundance data of pollen and spores, marine plankton and benthos were obtained from the same bulk samples collected along coastal sections in Yorkshire, UK, and combined with geochemical proxies of climate and environmental change derived from the literature.

We found that terrestrial ecosystems were more severely affected during the initial stages of the warming event, going through a gradual compositional change from wet-temperate to hot and drought-adapted species at the peak of warming. However, land plants recovered faster than marine communities, as temperatures and pCO₂ in the atmosphere decreased. Marine ecosystems experienced a more muted response to initial warming, but as warming peaked, marine plankton and benthic animals suffered a rapid and extreme turnover. The loss of large trees on land, which contributed to increase weathering, runoff and seawater eutrophication, and the development of anoxia, explain changes in the main primary producers (from dinoflagellate- to prasinophyte-dominated), and is also linked to the local disappearance of all infaunal species. Recovery for the marine realm was delayed compared to the land, especially for benthic forms that did not return to pre-warming diversity and structure even when the plankton had recovered to a dinoflagellate-dominated system. This study suggests that although ocean systems have a stronger buffering system to climate perturbations, and are initially more resilient than land plant ecosystems, they might be the last to recover, with a cascade effect from the planktonic to the seafloor environment.