Carbon mineralization of shelf and coastal sediments: A holistic approach using state of the art lander technology and the eddy-correlation technique.

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

Abstract

A significant fraction of the organic material produced or imported to our coastal seas is degraded within the sea-bed, a process mediated by infaunal invertebrates. The efficiency of this process has important implications for regional and global nutrient and element recycling. Benthic carbon mineralization represents the biogeochemical and biological conditions of marine ecosystems and can be readily measured. Ultimately, the fraction of material retained in the sediment record versus being degraded, regulates the CO2 and O2 concentration of our oceans (and atmosphere). The best and most widely used proxy for quantifying the benthic carbon mineralization is the benthic O2 exchange rate. Most commonly such rates are measured by chamber incubations or derived form high-resolution O2 microprofiles but, to obtain reliable data, measurements have to be performed directly at the seabed by so-called lander systems. Recently a new approach - the eddy-correlation technique - has been introduced to aquatic biology. The approach allows benthic O2 exchange rates to be quantified for several m2 of seabed and, unlike previous methodologies, is in principle non-invasive and does not affect potential regulating controls (i.e. hydrodynamics, light, fauna activity). In essence, the benthic O2 exchange is derived from simultaneous, rapid recordings of the unobstructed vertical current velocity and O2 concentrations in a small volume of water above the seabed. The technique is adapted from terrestrial research where it now represents a routine measurement for resolving gas exchange between ground and atmosphere (or aquatic areas and atmosphere). This novel approach overcomes the primary limitations of traditional approaches by integrating the signal from a large heterogeneous seabed and by not obstructing factors regulating the benthic exchange rates. Benthic chambers do, however, offer detailed insight on the benthic dynamic that not can be provided by the eddy-correlation approach. The three different approaches are thus truly complementary and together they provide powerful means of measuring ecosystem processes at ecosystem relevant scale. We propose concerted deployments of three benthic lander types to obtain benthic O2 exchange rates by microsensors, chambers and eddy-correlation. The two first lander types will be made available to the project while the latter will be realized within the project. Complemented with online camera surveys for characterizing the seabed and the macro- and mega fauna communities the measurements will provide detailed insight in the spatial variability of diagenetic activity from spatial scales of a few mm (transecting microprofile arrays), dm (chamber incubations), m (by eddy-correlation) to km by measuring along transects around topographic seabed structures. Temporal variations in benthic O2 exchange rates as induced by variations in regulating controls (hydrography, tide, turbidity, exchange of water masses, light, fauna activity) will be evaluated, in situ, by 1-5 days deployments of the developed eddy-lander and a transecting microprofiler. The eddy-lander will also be deployed in a number of hard-bottom environments (reefs, rocks) that generally not are assessable for chamber and microprofiling equipment to, for the first time, fully include these common, but rarely studied environments in estimates for coastal carbon turn over.

Publications

10 25 50

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Glud R (2009) Nitrogen cycling in a deep ocean margin sediment (Sagami Bay, Japan) in Limnology and Oceanography

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McGinnis D (2015) An Assessment of the Precision and Confidence of Aquatic Eddy Correlation Measurements in Journal of Atmospheric and Oceanic Technology

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Meysman F (2010) Oxygen penetration around burrows and roots in aquatic sediments in Journal of Marine Research

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Middelboe M (2011) Viral abundance and activity in the deep sub-seafloor biosphere in Aquatic Microbial Ecology

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Wenzhöfer F (2016) Benthic carbon mineralization in hadal trenches: Assessment by in situ O2 microprofile measurements in Deep Sea Research Part I: Oceanographic Research Papers

 
Description In short, we have developed and optimized a novel instrumentation for quantifying benthic solute exchange: Aquatic Eddy Covariance (AEC). The approach can non-invasively measure the exchange of e.g. O2 across the seabed. This is a key measure for understanding the biogeochemical functioning of marine ecosystems. We have deployed the instrumentation in a wide range of environment and provided new fundamental insight on benthic solute dynamics in many different marine habitats. This insight is fundamental for understanding how marine ecosystems respond to anthropogenic changes. AEC has a great potential for further advancing basic and applied research and will most likely be an important future monitoring tool.
Exploitation Route Our findings have been presented in 30 peer-reviewed manuscripts, and several international conferences. Several international research teams have contacted us and received training in these new measuring approaches in order to apply the for different research and monitoring tasks. This has also developed in to new collaborations and research projects. Companies are exploring the potential for commercialization.
Sectors Environment

 
Description The work has been included in teaching activities on undergraduate and graduate level
Sector Education,Environment
Impact Types Societal

 
Description GEOMAR EC 
Organisation Helmholtz Association of German Research Centres
Department Helmholtz Centre for Ocean Research Kiel
Country Germany 
Sector Academic/University 
PI Contribution The collaborators received substantial support and knowledge exchange in the area of sensing microeletrodes that were instrumental in the development and subsequent applications of the Aquatic Eddy Covariance (AEC) technique
Collaborator Contribution GEOMAR provided technical and logistical support both on the extensive deep-sea know-how and designing/building capacity of the institute facilities
Impact The multidisciplinary cooperation has lead to further advances of the Aquatic Eddy Covariance (AEC). Outcomes include the development of the next generation state-of-the-art AEC amplifiers for O2 microelectrodes and several peer-reviewed manuscripts ranging from deep-sea research to shelf sea research.
Start Year 2009
 
Description Danskernes Akademi 
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 Presentation entitled "The seabed; a microbial reactor with impact on the CO2 and O2 balance on earth" within the TV program "Danskernes Akademi" airing on the national Danish TV channel 2 (DR2). The presentations on the program aimed at informing the general public on globally relevant scientific topics, e.g. global warming, nutrient cycling and the associated research and research fields.
Year(s) Of Engagement Activity 2012
 
Description National History Museum 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Schools
Results and Impact This was an arrangement in National History Museum. The lecture with the title "The importance of bacteria communities in the deep sea" (30min was meant for an audience of 150 high-school students. One of the objectives was to rise awareness of the role on bacteria communities in deep-sea habitats using example from past and ongoing research.
Year(s) Of Engagement Activity 2013