Deep ocean communities impacted by changing climate over 24 y in the abyssal northeast Pacific Ocean

Abstract

The deep ocean, covering a vast expanse of the globe, relies almost exclusively on a food supply originating from primary production in surface waters. With well-documented warming of oceanic surface waters and conflicting reports of increasing and decreasing primary production trends, questions persist about how such changes impact deep ocean communities. A 24-y timeseries study of sinking particulate organic carbon (food) supply and its utilization by the benthic community was conducted in the abyssal northeast Pacific (∼4,000-m depth). Here we show that previous findings of food deficits are now punctuated by large episodic surpluses of particulate organic carbon reaching the sea floor, which meet utilization. Changing surface ocean conditions are translated to the deep ocean, where decadal peaks in supply, remineralization, and sequestration of organic carbon have broad implications for global carbon budget projections.carbon cycle | deep-sea ecology | climate change C ontemporary climate change marked by increasing water temperature, density stratification, and acidification is impacting the world ocean. These changes are especially evident in oceanic surface waters and coastal areas (1), where surface water production of organic carbon and trophic exchanges are affected. However, little is known of how these changes influence the food supply to the deep ocean. Can we expect decreased production of organic carbon produced in the upper ocean, and thus less food delivered to the sea floor? Because the deep ocean occupies the vast majority of the world, such answers are critical to evaluating impacts of climate variation on the global carbon cycle, particularly regarding long-term carbon sequestration.A major unknown component of the global carbon cycle is the amount of organic carbon that reaches the deep ocean and its ultimate utilization or long-term sequestration in the sediments. This supply starts with primary production by phytoplankton in surface waters. There is no consensus on whether phytoplankton biomass is decreasing as a result of a reduction in upwelled nutrients, caused by warming surface waters and increasing stratification (2). In open ocean areas, these conditions can lead to a decrease in primary production by phytoplankton (1, 3) and a geographic expansion of oligotrophic (low chlorophyll) waters (3). In contrast, along-shore winds and increased land-sea temperature disparities are leading to increased nutrient supply and primary production in coastal upwelling areas (1, 2, 4-6). A portion of the organic carbon produced in surface waters is exported to the deep ocean by a variety of mechanisms, including mineral ballasting, aggregation, fecal pellet production, and sinking or vertical migration of large zooplankton (7)(8)(9)(10)(11)(12).How do such conditions impact the food supply to the deep ocean, which relies on surface water primary production? Previous studies have shown an unexpected shortage of food reaching deep ocean depths to sustain benthic communities over an 18-y period, with...

Major impacts of climate change on deep-sea benthic ecosystems

“…Many observational studies are showing that presentday climate change is already impacting deep-sea environments, as evidenced by increased deep-sea temperature (Purkey and Johnson, 2010), deoxygenation (Stramma et al, 2008(Stramma et al, , 2010(Stramma et al, , 2012Keeling et al, 2010;Helm et al, 2011), lowered pH of intermediate deep-waters (Byrne et al, 2010), and altered POC flux to the seafloor (Ruhl and Smith, 2004;Smith et al, 2013). Despite emerging evidence that climate-driven changes in deep-sea environmental conditions may perturb the functioning of oceanfloor ecosystems (Danovaro et al, 2001;Smith et al, 2007Dunlop et al, 2016;, our understanding of the extent to which projected physical and chemical changes will lead to deleterious ecological consequences is still very poor (Philippart et al, 2011).…”

Algal pigments in Southern Ocean abyssal foraminiferans indicate pelagobenthic coupling

“…The quality and quantity of this input, the pelago-benthic coupling, will determine the structure and function of the communities (Dayton et al, 1994;Epping, 2013;Fabiano et al, 1997;Gooday, 2002;Graf, 1989;Graf et al, 1995;Grebmeier et al, 1988;Grebmeier and Barry, 1991;Hughes et al, 2007;Schnack-Schiel and Isla, 2005;Smith et al, 2006Smith et al, , 2013. This input occurs as sinking of particles produced at the surface (Asper et al, 1992;Fabiano et al, 1997).…”

Decadal Change in Sediment Community Oxygen Consumption in the Abyssal Northeast Pacific

“…These values were then converted into organic carbon using a respiratory quotient of 0.85 for mixed carbohydrate and lipid with final units given as mg C m -2 day -1 (Smith et al 1979). Synchronous deployments of SCOC monitoring instrumentation have confirmed the resulting measurements do not differ significantly, and can be compared in analyses of seasonal and yearly patterns in SCOC [FVGR andTCR compared in Fall 1994 andSpring 1995;FVGR and Rover I compared in Spring 1996;FVGR andRover II compared in Fall 2011 (Smith andSmith et al 1997Smith et al , 2013]. SCOC and POC flux were averaged for one-month periods (referred to as ''monthly average'').…”

“…The use of image-based estimations of carbon dynamics is a particularly promising avenue for augmenting sediment trap sampling in the estimation of POC flux. For example, there are now multiple approaches for quantifying POC from imagery across a range of particle types and sizes (e.g., Iversen et al 2010;Briggs et al 2011;Cetinić et al 2012;Smith et al 2013;Dall'Olmo and Mork 2014).…”

“…Rover I was lost during a mission in the central Pacific in 1999. Rover II development began shortly afterward, and this vehicle has been in operation since 2011 (McGill et al 2009;Sherman and Smith 2009;Smith et al 2013Smith et al , 2014. Synoptic measurements of SCOC between many of these instruments have yielded comparable fluxes with no significant differences (Smith et al 1997Smith and Kaufmann 1999), allowing for long-term changes to be assessed.…”