Land-sea ecological connectivity during a Jurassic warming event

Silvia Danise,Sam M Slater,Vivi Vajda,Richard J Twitchett

doi:10.1016/j.epsl.2021.117290

Abstract

Knowledge on how climate change affects land-sea ecological connectivity in deep time is scarce. To fill this knowledge gap we have assembled a unique dataset through a Jurassic (early Toarcian) warming event that includes quantitative abundance data from pollen and spores, organic-walled marine plankton and benthic macro-invertebrates, in association with geochemical data derived from the same sampled horizons, from the Cleveland Basin, UK. Using this dataset we: (i) reconstruct the timing of degradation and recovery of land-plants, marine primary producers and benthic fauna in response to this event, and (ii) test for connectivity between changes in land and marine ecosystems. We find a discrepancy between the timing of the response of land-plant and marine ecosystems to the event. Land-plants were the first to be affected by initial warming, but also recovered relatively quickly after the peak of warmth to return to pre-event levels of richness and diversity. Plankton and benthic fauna instead experienced a delayed response to initial warming, but as warming peaked, they suffered a rapid and extreme turnover. Recovery in the shelf sea was also delayed (particularly for the benthos) compared to the vegetation. Ecological connectivity analyses show a strong link between changes in terrestrial and marine ecosystems. The loss of large trees on land contributed to changes in marine plankton, from dinoflagellate- to prasinophyte algal-dominated communities, by enhancing erosion, runoff and nutrient-supply into shallow seas. Eutrophication and changes in primary productivity contributed to the decrease of dissolved oxygen in the water column and in bottom waters, which in turn affected benthic communities. Such cause-effect mechanisms observed in the Cleveland Basin are likely to have occurred in other basins of the Boreal Realm, and in part also in basins of the Sub-Boreal and Tethyan realms. Although palaeolatitudinal and palaeoceanographic gradients may have controlled local and regional changes in land-plants and marine ecosystems during the Early Jurassic, the main climatic and environmental changes linked to rapid global warming, enhanced weathering and high primary productivity, are shared among all the examined realms.

Highlights

In the near future, species are likely to experience climates for which no current analogue exists, with future projections indicating a potentially catastrophic loss of biodiversity (Trisos et al, 2020)
Combined analyses of relative abundances, richness and diversity (Fig. 2), with multivariate ordinations (Fig. 3), enable the comparison between land-plants, marine plankton and benthic fauna through the early Toarcian event (eTe) to be examined at the species- and communitylevel for the Cleveland Basin composite section (Fig. 4)
Ering and run-off had on primary productivity during the early Toarcian event

Summary

Introduction

Species are likely to experience climates for which no current analogue exists, with future projections indicating a potentially catastrophic loss of biodiversity (Trisos et al, 2020). Temperature rise, has a critical impact on both terrestrial and marine ecosystems, which are closely linked by physical, chemical and biological processes (Fang et al, 2018). Understanding how land and marine environments respond differently to climate change in the long-term, and how climate change influences links between these environments is critical for developing whole-ecosystem response models for the long-term impacts of climate change (Häder and Barnes, 2019). We utilise the early Toarcian event (eTe; Early Jurassic, ∼183 million years ago, Ma) as a model system for exploring how land-sea connectivity responds to climate change.

Objectives

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Results

Conclusion