Impact of the Geometry of Submarine Landscapes on Deep-Sea Biogeochemistry

Lead Research Organisation: Scottish Association For Marine Science
Department Name: Scottish Association For Marine Science

Abstract

Production of organic carbon by phytoplankton in the surface ocean, followed by transport of some of this organic carbon on sinking particulate matter from the surface ocean into underlying sediments, extracts carbon dioxide from and injects oxygen into the atmosphere. For long geological time scales of thousands up to hundreds of millions of years it is believed that changes in the magnitude of organic-carbon deposition in deep-sea sediments can influence the chemical composition of the atmosphere. Organic-carbon burial in deep-sea sediments must, therefore, be one of the key processes of the 'life-supporting system' on Earth. Consequently, an understanding of the mechanisms controlling the flux of carbon from the oceanic water column into underlying sediments and the burial of carbon in the sediments is of crucial importance. A number of possible controls on these carbon fluxes into deep-sea sediments have been studied. However, to date the impact of submarine landscape geometry has received virtually no attention. This is despite comprehensive and pervasive submarine landscape changes that must have occurred as a result of the rearrangements of continents and oceanic crust during the last hundreds of millions of years. Mid-ocean ridges, but also to some degree abyssal plains, are structured by submarine hills and mountains. Such kilometre-scale seafloor elevations are a major source of environmental variability in the deep sea. In addition to their mere presence, the interaction of the elevations with quasi-steady background (residual) and tidal flow introduces complexity in the environment. This enhanced complexity is expected to influence a range of environmental parameters and processes, including larval dispersal of deep-sea organisms, biodiversity (an important indirect control on sediment biogeochemistry), the absolute magnitude of sedimentary carbon burial, and the relative proportions of organic carbon being remineralised in deep-ocean waters and surface sediments versus organic carbon being buried in deeper sediments. This project will elucidate for the first time the link between three fundamental aspects of kilometre-scale flow/topography interactions and organic-carbon dynamics in the deep ocean: (1) The influence of the PRESENCE OF A SEAMOUNT on the transport of organic carbon through the water column and its fate in deep-sea sediments. (2) The impact of GEOGRAPHICAL LATITUDE: Quasi-steady background flow interacts with the seamount, with the shape of the resulting flow field depending on the impact of the Earth's rotation which, in turn, depends on the geographical latitude of the seamount. Are there latitudinal differences in the impact of topographically controlled flow fields on carbon dynamics? (3) The impact of TIDES: Tidal current velocities vary spatially in the deep sea and may have varied temporally over ice age cycles, thereby introducing spatiotemporal variability in the magnitude of tidal impact. How do different tidal forcings influence carbon dynamics at kilometre-scale seafloor elevations? We propose to elucidate these three problems by comparing seamounts of similar dimensions which differ in terms of their geographical latitude and tidal forcing: In the Northeast Atlantic the Senghor Seamount at 17degN and the Ampere Seamount at 35degN have similar open-ocean tidal forcing and can be compared in terms of the impact of the geographical latitude; the Ampere Seamount at 35degN and the Eratosthenes Seamount in the Eastern Mediterranean at 33.5degN are at similar geographical latitude and can be compared in terms of tidal forcing, with the tides in the Eastern Mediterranean being much weaker than the tides in the Northeast Atlantic. The main anticipated achievement of this project is a much advanced understanding of the fundamental controls of seafloor geometry on deep-sea biogeochemistry and biodiversity.

Publications

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Kessler AJ (2013) Transport zonation limits coupled nitrification-denitrification in permeable sediments. in Environmental science & technology

 
Description This project has been looking into the influence of submarine mountains, hills and trenches on the formation of seafloor sediments and the diversity of biological communities living in the sediments. Through their interactions with different types of ocean flow components (tidal, near-inertial and basin-scale bakcground currents), intermediate-scale submarine topographic features introduce a substantial level of spatial environmental variability at spatial scales of hundreds of meters up to tens of kilometers. Biogeochemical and biological processes and patterns at these scales had not been studies in any systematic ways before.

Analyses of the project results are still ongoing. But outcomes so far indicate that, because of the large number of such seafloor features in the global ocean, their presence is expected to be a so-far under-appreciated factor in determining biodiversity in the deep seas.

So far, there have been two biogeochemical key findings. First, flow/topography interactions control the chemical composition and quantity of depositing sediments. This applies to topographic features as varied as abyssal hills and hadal trenches and has implications for our understanding of (1) how food is supplied to the organisms living on and in the seafloor, (2) how chemical elements of global biogeochemical relevance are buried in deep-sea sediments, and (3) how sedimentary records of past environmental change are formed. The second key finding is that, for the above processes and phenomena, tidal flow components are often more important than the basin-scale background flow component that has been invoked in the past to explain sediment dynamics in the deep sea.
Exploitation Route There are several types of mineral deposit in the deep seas that are associated with submarine topographic features and of potential economic interest. One of them is iron-manganese crusts that can grow, for instance, on the slopes of seamounts.

One main application of the anticipated overall results of this project is a better mechanistic understanding of where these crusts are likely to be found, with potential implications for future exploration of these crusts and for guiding their most sustainable exploitation.
Sectors Aerospace, Defence and Marine,Education,Environment,Security and Diplomacy

 
Description Results from this project are still in the process of being analysed and consolidated. We, however, expect the final output to be of relevance to a more nuanced regulation and implementation of the exploitation of natural resources in the deep seas.
 
Description Deep-Sea Forum Small Grants scheme
Amount £990 (GBP)
Organisation Marine Alliance for Science and Technology for Scotland 
Sector Academic/University
Country United Kingdom
Start 11/2014 
End 11/2015
 
Description ERC Advanced Grant
Amount € 157,500 (EUR)
Funding ID 669947 - HADES - ERC-2014-ADG/ERC-2014-ADG 
Organisation European Research Council (ERC) 
Sector Public
Country Belgium
Start 01/2016 
End 01/2021
 
Description NERC PhD studentships
Amount £71,800 (GBP)
Organisation Natural Environment Research Council 
Sector Public
Country United Kingdom
Start 09/2012 
End 02/2016
 
Description Recent sediment dynamics in hadal trenches
Amount £980 (GBP)
Organisation Marine Alliance for Science and Technology for Scotland 
Sector Academic/University
Country United Kingdom
Start 06/2013 
End 03/2014
 
Description High rates of microbial carbon turnover in sediments in the deepest oceanic trench on Earth_01 
Form Of Engagement Activity A press release, press conference or response to a media enquiry/interview
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Public/other audiences
Results and Impact Live radio interview on BBC Radio 5 Live

Informing the general public about life at the greatest depths of the ocean.
Year(s) Of Engagement Activity 2013
 
Description High rates of microbial carbon turnover in sediments in the deepest oceanic trench on Earth_02 
Form Of Engagement Activity A press release, press conference or response to a media enquiry/interview
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Public/other audiences
Results and Impact Live radio interview with BBC Radio 4

Informing the general public about life at the greatest depths of the ocean.
Year(s) Of Engagement Activity 2013
 
Description High rates of microbial carbon turnover in sediments in the deepest oceanic trench on Earth_03 
Form Of Engagement Activity A press release, press conference or response to a media enquiry/interview
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Public/other audiences
Results and Impact Pre-recorded radio interview with BBC World Service

Informing the general public about life at the greatest depth of the ocean.
Year(s) Of Engagement Activity 2013
 
Description High rates of microbial carbon turnover in sediments in the deepest oceanic trench on Earth_04 
Form Of Engagement Activity A press release, press conference or response to a media enquiry/interview
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Public/other audiences
Results and Impact Live radio interview with BBC Radio Scotland

Informing the general public about life at the greatest depths of the ocean.
Year(s) Of Engagement Activity 2013
 
Description High rates of microbial carbon turnover in sediments in the deepest oceanic trench on Earth_05 
Form Of Engagement Activity A press release, press conference or response to a media enquiry/interview
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Public/other audiences
Results and Impact Live radio interview with BBC Radio Wales

Informing the general public about life at the greatest depths of the ocean.
Year(s) Of Engagement Activity 2013
 
Description High rates of microbial carbon turnover in sediments in the deepest oceanic trench on Earth_06 
Form Of Engagement Activity A press release, press conference or response to a media enquiry/interview
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Public/other audiences
Results and Impact Pre-recorded radio interview with The Voice of Russia

Informing the general public about life at the greatest depths of the ocean.
Year(s) Of Engagement Activity 2013
 
Description High rates of microbial carbon turnover in sediments in the deepest oceanic trench on Earth_07 
Form Of Engagement Activity A press release, press conference or response to a media enquiry/interview
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Public/other audiences
Results and Impact Pre-recorded radio interview with the Austrian broadcaster FM4 ORF

Informing the general public about life at the greatest depths of the ocean.
Year(s) Of Engagement Activity 2013
 
Description High rates of microbial carbon turnover in sediments in the deepest oceanic trench on Earth_09 
Form Of Engagement Activity A press release, press conference or response to a media enquiry/interview
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Public/other audiences
Results and Impact pre-recorded interview with PRI's The World - Global Perspectives for an American Audience

Informing the general public about life at the greatest depths of the ocean.
Year(s) Of Engagement Activity 2013
 
Description High rates of microbial carbon turnover in sediments in the deepest oceanic trench on Earth_10 
Form Of Engagement Activity A magazine, newsletter or online publication
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Public/other audiences
Results and Impact reporting of this story in 60 other mainly international media outlets

Informing the general public about life at the greatest depths of the ocean.
Year(s) Of Engagement Activity 2013
 
Description Mountains of the deep 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Schools
Results and Impact Presentation given to high school students. School visit.

Interest of school leavers in science degrees, including the one at SAMS.
Year(s) Of Engagement Activity 2012
 
Description Seamount research 
Form Of Engagement Activity Participation in an open day or visit at my research institution
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Public/other audiences
Results and Impact SAMS Open Day

Interest of local / regional school leavers in science degrees, including the one at SAMS.
Year(s) Of Engagement Activity 2012
 
Description Underwater Mountains 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Public/other audiences
Results and Impact Oral presentation at Oban Highland Games

Interest of school leavers in science degrees, including the one at SAMS.
Year(s) Of Engagement Activity 2012