What the geological past can tell us about the future of the ocean’s twilight zone

Abstract

Paleontological reconstructions of plankton community structure during warm periods of the Cenozoic (last 66 million years) reveal that deep-dwelling ‘twilight zone’ (200–1000 m) plankton were less abundant and diverse, and lived much closer to the surface, than in colder, more recent climates. We suggest that this is a consequence of temperature’s role in controlling the rate that sinking organic matter is broken down and metabolized by bacteria, a process that occurs faster at warmer temperatures. In a warmer ocean, a smaller fraction of organic matter reaches the ocean interior, affecting food supply and dissolved oxygen availability at depth. Using an Earth system model that has been evaluated against paleo observations, we illustrate how anthropogenic warming may impact future carbon cycling and twilight zone ecology. Our findings suggest that significant changes are already underway, and without strong emissions mitigation, widespread ecological disruption in the twilight zone is likely by 2100, with effects spanning millennia thereafter.

Deep‐pelagic fishes: Demographic instability in a stable environment

“…The availability of organic carbon at depth may be evident in the fossil record (Boscolo‐Galazzo et al., 2021). Deep‐pelagic formaninifera diversity and abundance increases as ocean temperatures decrease, a feature attributed to a greater volume of food reaching this habitat (Boscolo‐Galazzo et al., 2021; Crichton et al., 2023). This increase in food availability would be expected to positively benefit population sizes for the other members of the deep‐pelagic food web, including fish species.…”

“…Vertically migrating fishes in the upper mesopelagic typically forage in surface waters where the food web is supported by recent in situ primary production (Gloeckler et al., 2018; Sutton & Hopkins, 1996). In contrast, some non‐migratory fishes that reside in the lower mesopelagic and the bathypelagic largely rely on a suspended, particle‐based food web composed of degraded particulate organic matter originating in the epipelagic (Crichton et al., 2023; Eduardo et al., 2023; Gloeckler et al., 2018; Hannides et al., 2020). Thus, the amount of carbon available to non‐migratory consumers in the lower mesopelagic and bathypelagic zones is directly linked to the amount of primary production in surface waters and the rate at which it can reach deeper depths.…”

“…Changes in ocean temperatures can greatly alter the amount of the particulate organic carbon (POC) that reaches this environment, in turn affecting the amount of food available to support this community (Crichton et al, 2023;John et al, 2013;Olivarez Lyle & Lyle, 2006). Crichton et al (2023) suggest that bacteria may drive this phenomenon. As oceans warm the metabolic rates of bacteria increase, leading to greater consumption of sinking organic material, and less POC reaching deep waters (Crichton et al, 2023).…”

“…Changes in ocean temperatures can greatly alter the amount of the particulate organic carbon (POC) that reaches this environment, in turn affecting the amount of food available to support this community (Crichton et al, 2023;John et al, 2013;Olivarez Lyle & Lyle, 2006). Crichton et al (2023) suggest that bacteria may drive this phenomenon.…”

Combating Climate Change and Global Warming for a Sustainable Living in Harmony with Nature

“…Bumble bees which depend on wildflowers for their survival can also be affected as extremely high temperatures have negatively impacted most species of them over the past 120 years [55] . If greenhouse gas emissions and warmer temperatures are not controlled, some researchers estimate that life in oceans could be depleted severely within the coming 150 years [56] . The risk of species loss depends on how far global temperatures rise in the future.…”