Response of seafloor ecosystems to abrupt global climate change

Abstract

Anthropogenic climate change is predicted to decrease oceanic oxygen (O 2 ) concentrations, with potentially significant effects on marine ecosystems. Geologically recent episodes of abrupt climatic warming provide opportunities to assess the effects of changing oxygenation on marine communities. Thus far, this knowledge has been largely restricted to investigations using Foraminifera, with little being known about ecosystem-scale responses to abrupt, climate-forced deoxygenation. We here present high-resolution records based on the first comprehensive quantitative analysis, to our knowledge, of changes in marine metazoans (Mollusca, Echinodermata, Arthropoda, and Annelida; >5,400 fossils and trace fossils) in response to the global warming associated with the last glacial to interglacial episode. The molluscan archive is dominated by extremophile taxa, including those containing endosymbiotic sulfur-oxidizing bacteria (Lucinoma aequizonatum) and those that graze on filamentous sulfur-oxidizing benthic bacterial mats (Alia permodesta). This record, from 16,100 to 3,400 y ago, demonstrates that seafloor invertebrate communities are subject to major turnover in response to relatively minor inferred changes in oxygenation (>1.5 to <0.5 mL·L −1 [O 2 ]) associated with abrupt (<100 y) warming of the eastern Pacific. The biotic turnover and recovery events within the record expand known rates of marine biological recovery by an order of magnitude, from <100 to >1,000 y, and illustrate the crucial role of climate and oceanographic change in driving long-term successional changes in ocean ecosystems.seafloor ecosystems | abrupt climate change | deglaciation | oxygen minimum zone | metazoans O ceanic deoxygenation is a predictable, fundamental, and long-lasting property of anthropogenic climate change (1). The global ocean inventory of oxygen is predicted to decline between 1% and 7% by the year 2100, and modeling predictions reveal extensive oceanic deoxygenation, on thousand-year timescales, under "business-as-usual" carbon emission scenarios (2). Modern oceanographic time series already document rapid loss of [O 2 ] in interior ocean waters over the last 4 decades (3, 4), although this trend is complicated in regions where [O 2 ] demand is decreased through the slackening of trade winds (5). As oxygen levels in the ocean decrease and the already extensive oxygen minimum zones (OMZs) expand, the volumetric habitat for aerobic respiration is reduced, presumably resulting in a fundamental reorganization of marine communities. Past events of climate warming and OMZ expansion, including the recent deglaciation from 18 to 11 ka, provide a case study for understanding the effects on marine ecosystems of abrupt temperature and oxygenation changes.Paleoceanographic records clearly demonstrate that OMZ strength changed in response to

Contrasting futures for ocean and society from different anthropogenic CO 2 emissions scenarios

“…Avoiding very high levels of risk requires limiting the increase in global surface temperature between 1990 and 2100 to below 2°C and the increase in SST below~1.2°C. These risks of impact, based on perturbation experiments, field observations, and modeling, are consistent with the paleorecord, which indicates mass extinctions triggered by carbon perturbation events such as at the Permo-Triassic boundary [at a rate slower than the present one (98)] or severe losses of deep-sea fauna during the last glaciation, attributed to oxygen depletion (99). Evolution in response to environmental changes that occurred much slower than those projected in the coming decades did not, therefore, prevent major largescale alterations of marine ecosystems.…”

Biodiversity response to natural gradients of multiple stressors on continental margins

“…Oxygen concentration is the predictor variable that best explains variance, with diversity in communities living below 0.16 ml l 21 O 2 (7 mM) around half that at higher oxygen concentrations (table 1; average H 0 of 2.1 versus 4.0 in low-and high-O 2 partitions). This oxygen level is similar-within available precision-to macrofaunal oxygen thresholds identified in the Pleistocene fossil record of the Santa Barbara Basin [12]. Further, this is the oxygen level identified on the Pakistan margin below which foraminifera-dominated processing of particulate organic matter occurs (relative to macrofauna), pointing to potential direct or indirect functional links between diversity and organic matter cycling [26].…”

“…The upper and lower boundaries of oxygen minimum zones (OMZs) support strong zonation of communities, with rapid shifts in faunal diversity that are clearly responding to hydrographic changes, often in a threshold-like manner [17,18]. In many instances, the resident fauna have had long periods of time (millions of years [19]) to adapt to the extreme conditions found within OMZs, although they can be dynamic on glacial/interglacial (10 000 years) [20] or much shorter [12] time scales. In this study, we exploit naturally occurring hydrographic gradients across upwelling margins to examine the potential influence of environmental variables on the community structure of continental margin macrobenthos ( polychaetes, crustaceans, molluscs, echinoderms and other invertebrates).…”

Major impacts of climate change on deep-sea benthic ecosystems

“…For example, in the bathyal Santa Barbara Basin (California margin), rapid, alternated shifts in the seafloor ecosystem have occurred in response to changes in OMZ intensity associated with D-O and de-glacial abrupt warming events Moffitt et al, 2015a). North Atlantic fossil records during the last de-glaciation showed abrupt changes in deep-sea biodiversity associated with a rapidly changing climate (specifically deep-water circulation and temperature) over decadal to centennial time-scales (Yasuhara et al, , 2014.…”