IAP-24-045

Role of turbidity currents in organic carbon and nutrient transport to deep-sea environment

Powerful seabed sediment flows called turbidity currents form the largest sediment accumulations, deepest canyons and longest channels on Earth. These flows transfer vast amounts of detrital sediment and organic carbon to the deep sea. Organic carbon (OC) burial in marine sediments is identified as the second-largest sink of atmospheric CO2 (Smith et al., 2015), but the role of turbidity currents is typically overlooked. Majority of the studies consider only the top 30-50cm and mostly fine-grained deposits. However, our work shows that coarser grained turbidity current deposits transfer and bury considerable amount of organic carbon (Hage et al., 2020 and 2022). Particularly, the fine sand/silt grain size fraction of turbidites identified as rich in young terrestrial organic carbon. In addition to grain size control on organic carbon distribution, turbidity currents are also rich in extracellular polymeric substance (EPS). This cohesive substance is formed by microorganisms typically to attach themselves to sediment surface and transfer nutrients. Studies estimate that EPS makes up the 40% of total organic carbon transported to the deep sea (Craig et al., 2020), however contribution of turbidity currents are not included. EPS is adhesive and hence facilitates clay flocculation, formation of clay-coated sand grains and, binding of organic matter and nutrients to sediment (Craig et al., 2020; Duteil et al., 2020). Our previous study at Bute Inlet (BC, Canada) suggested that most EPS is formed by benthic diatoms, most likely at the delta top, and later transported to deep sea (above 600m water depth) by turbidity currents. In some deposits, EPS makes up the majority of the total organic carbon fraction of the sediments.
The efficient transport of EPS and organic carbon to deep sea mostly results in quick burial of organic carbon. Additionally, this process provides extra nutrient to distal lobes, situated at the mouth of submarine channels. High influx of organic matter and EPS-bound nutrients likely to support unexpected ecosystem development in these areas, such as the localised communities at distal lobe that lies beyond the termination of the Congo Canyon (Baudin et al., 2017).
This PhD project aims to understand EPS related organic carbon budget and nutrient transport pathways to deep-sea. The project will utilise a comprehensive sample set collected on 2019 and 2023 Congo Cruises funded by NERC (NE/R001952/1) as well as 2021 and 2022 Bute Inlet samples. In the context of the NERC project, there might be opportunities to join a marine research cruise for further data collection. The candidate will join the wider UK and international researcher community of submarine sediment and OC transport projects. This will provide opportunity to develop excellent communication and team player skills. Academic and analytical skills will involve understanding of carbon cycle, sediment transport processes and climate modelling as well as organic geochemistry, core logging, and clay mineralogy.

In this project, various sedimentological and chemical analytical techniques will be used. Total Organic Carbon (TOC), nitrogen, total carbon and EPS quantification along with carbon isotope composition (13C) will make the first analytical techniques to quantify and characterise the organic carbon content. 14C dating will be used to date the organic carbon from various sedimentary facies. Dating will support to quantify young vs reworked organic carbon. Other sedimentological techniques will include core logging, grain size analysis, and clay mineral identification. GIS techniques, handling large datasets (such as bathymetry data), statistics and quantitative modelling will also be used during the data collection and interpretation. Support and training will be these methods will be provided during the PhD.

Year 1

First 6 months of the project will focus on literature review, data management, sample identification and familiarizing with analytical and GIS techniques. First textural and mineralogical sediment characterisation will take place in the second half of Year-1. This analysis will include clay mineralogy, sandstone petrography and grain size analysis.

Year 2

Majority of the Year-2 will be dedicated to laboratory work including identification of TOC, C-N-S values of the sediment, isotopic composition of organic carbon fraction and EPS quantification with total carbohydrate and chlorophyl content of sediments. Radiocarbon dating will be used to date old cores. First draft of first manuscript should be ready to be circulated through co-authors.

Year 3

Organic carbon and EPS charaterisation will continue through the Year-3. Majority of this year will be used to finalising first and preparing the second manuscript for publication, finalising all the lab work and dissemination of results in appropriate international symposiums.

Year 3.5

This 6 months will mainly focus on writing up the thesis and preparing illustrations for the final submission.

During the lifespan of the project, student will be provided relevant training for spatial data handling (GIS, bathymetry), sedimentary lab and petrography techniques (clay mineralogy, sedimentary petrography, textural analysis), geochemical methods (TOC, CNS, d13C etc). Besides these, student will be expected to follow some courses which will be provided by Newcastle University, focusing on knowledge and intellectual abilities, personal effectiveness, research governance and organisation, engagement and impact.

Supervisor team is supportive of student’s personal development and believes the importance of attending national and international symposiums, presenting their work, and discussing with other researchers in the area. The student will be encouraged to attend scientific meetings. They will also be join a wider research team, which will support them with personal and scientific development.