Primary productivity controls on opportunistic bivalves during Early Jurassic oceanic deoxygenation

Abstract

Severe paleoclimatic change during the Toarcian (Early Jurassic) oceanic anoxic event (OAE) was characterized by a negative δ 13 C excursion, increased weathering, higher seawater temperatures, oceanic deoxygenation, and mass extinction. We present abundance and size data (n ≈ 36,000) for the two dominant epifaunal bivalve species from the Toarcian OAE, Yorkshire, UK. We statistically correlate the biotic data with geochemical proxies for environmental change and show that our results are comparable with changes in present-day ecosystems affected by hypoxia. Bositra radiata dominated during declining oxygen levels immediately before the Toarcian OAE sensu stricto, and shell size doubled when δ 13 C org was decreasing, indicating a connection with primary productivity. Small Pseudomytiloides dubius dominated during the Toarcian OAE and varied sharply in abundance, indicating that it was highly opportunistic. P. dubius shell size is strongly related to Mo concentration, [Mo]; this indicates a relationship between size and N 2 -fi xing primary productivity via [Mo] limitation. A secondary factor contributing to small shell size was lower oxygen levels. After the Toarcian OAE diversity increased, P. dubius was less abundant and shell size doubled, indicating that bivalve populations were less limited by resources and conditions were more favorable. Size frequency distributions show that bothToarcian species had short life spans, rapid generation times, high recruitment, and high juvenile mortality. The opportunist Mulinia lateralis is a present-day analog for P. dubius. This research provides a case study for the long-term impacts of deoxygenation upon marine ecosystems, including that being observed today.

Development of the freeze–thaw processing technique for disaggregation of indurated mudrocks and enhanced recovery of calcareous microfossils

“…The freeze-thaw method resulted in both a better breakdown of the indurated mudrocks compared to other standard methods and, when combined with white spirit and sodium hexametaphosphate, produced a more abundant and diverse assemblage of the foraminifera preserved in the sediment with no evidence of damage to the tests. To test the freeze-thaw method, we used organic-rich, indurated mudrocks that were deposited prior to and during the Toarcian (Early Jurassic) Oceanic Anoxic Event (Kemp et al 2005(Kemp et al , 2011Caswell & Coe, 2013). Our results also extend the range of one foraminifer compared to that reported by Hylton (2000, unpublished PhD thesis, University of Plymouth).…”

Is long-term ecological functioning stable: The case of the marine benthos?

“…The KCF represents the longest period (~8 million years; Weedon et al, 2004) of organic carbon accumulation during the Mesozoic (Jenkyns et al, 2002) although not the most severe (cf. Caswell and Coe, 2013), and was deposited under fluctuating levels of oxygenation (Pearce et al, 2010) that ranged from hypoxic (low dissolved oxygen, 1-30% of saturation) to anoxic (the absence of oxygen) to euxinic (oxygen absent and toxic H 2 S present).…”

Multiphase response of palynomorphs to the Toarcian Oceanic Anoxic Event (Early Jurassic) in the Réka Valley section, Hungary

“…Harries and Little, 1999;Pálfy and Smith, 2000;Wignall, 2001;Caruthers et al, 2013;Caswell and Coe, 2013;Danise et al, 2013). Coeval environmental perturbations include increased terrestrial input due to enhanced weathering and riverine influx, stratification of the water column with subsequent anoxia and ocean acidification.…”