Progress and achievements of Shelf Sea Biogeochemistry research programme from biannual summary reports to NERC, 2014-2017

September 2017

Iron in short supply in UK seas

Iron is one of the commonest elements in the Earth’s crust, and it is essential for both plants and animals. However, seawater concentrations are usually very low, due to its relative insolubility when oxidised. In the open ocean, particularly in the Southern hemisphere, iron is often the main factor limiting the abundance of primary production (by phytoplankton) and hence all other marine life. Until recently, such iron limitation was not thought to affect shelf seas in the North Atlantic. However, researchers from the University of Plymouth and others supported by the SSB programme have now shown 1 that seasonal shortages of iron can occur in the central Celtic Sea, under conditions of reduced summer mixing. These novel findings were made possible by using ultra-clean sampling techniques, with separate analyses of dissolved, colloidal and particulate iron at different depths of the water column. Such iron deficiencies do not necessarily reduce total marine productivity; nevertheless, species successions and community composition are likely to be affected. Provisional results 2 from the Hebridean shelf (off NW Scotland) indicate that seasonal iron limitation could be even more pronounced, and hence of greater ecological importance, in more northerly UK seas.

Special Issue of Biogeochemistry on seafloor cycling

Ten papers authored by more than 60 SSB researchers have been published together in a Special Issue of the journal Biogeochemistry,3 with main findings summarised in an article in Impact magazine.4 These studies provide new insights on benthic processes: how the seafloor cycling of carbon, oxygen, nitrogen and iron can at some times of year remove (and bury), and at other times return, biologically-important elements to shelf seas around the UK. Most of the results are from samples and data collected on the SSB cruises in the Celtic Sea in 2014 and 2015. A range of sediment types, ranging from sand to mud, were investigated: they were found to have significantly different biogeochemical characteristics, e.g. in terms of oxygen and nitrogen dynamics, and pH profiles, influenced not only by seasonal temperature changes, but also by variable organic carbon inputs, physical disturbance, and differences in microbial and invertebrate community composition. These interactions and their temporal variability can now be simulated in an improved version of the shelf sea ecosystem model, ERSEM. There is, however, still scope for model improvement, e.g. in distinguished a relatively large (>90%) component of benthic organic carbon that is apparently inactive.

Final SSB Science Meeting; other meetings and conferences

The Final Science Meeting of the SSB programme was held at the University of Winchester, 5-6 June 2017. This provided the opportunity for SSB researchers to present their individual results and conclusions, with 40 short talks, and 16 posters; it also gave momentum to the process of bringing that information together for more integrated assessments, both within and between Work Packages. To facilitate that integrative effort, and thereby maximise SSB outcomes and benefits, NERC and Defra agreed to support an additional synthesis and dissemination funding round, with focus on cross-programme science-to-policy aspects. Supplementations for five projects, with associated short extensions for some awards, were subsequently approved. Their total value is ~£240k (at 80% FEC), for completion in FY 2017-18.

In addition to SSB presentations5 given at the Challenger AMBIO VIII meeting2, three SSB oral presentations were given at the 19th European Geosciences Union (EGU) General Assembly and science conference, Vienna 23-28 April, by J Jardine et al; C Williams et al and Humphreys et al.

February 2017

From rivers to open ocean: what happens to nutrients in between?

As on land, primary production (plant growth) in the ocean depends on a supply of nutrients, particularly soluble forms of nitrogen (N) and phosphorus (P). In rivers, levels of such nutrients can be high – but do they actually reach the open ocean, or are they retained in estuaries and shelf seas? Faced with the complexity of many thousands of geochemically-different rivers and coastal systems, most global models of N and P cycling have to date made simplistic all-or-none assumptions. A new study6 by SSB researchers (Work Package 1) and international colleagues combines empirical data for river nutrient loads and nutrient removal rates with mechanistic models for the residence times of low-salinity river plumes in shelf seas: they found that globally around 75% of soluble nitrogen and 80% of soluble phosphorus delivered by rivers is likely to reach the open ocean. The main uncertainties related to exchange rates across the shelf break and nutrient processing dynamics, two issues directly addressed for UK waters by the SSB field programme.

Trawling effects on benthic invertebrates and biogeochemistry

Trawling necessarily disturbs the seafloor. It affects the physical structure of sediments, as well as the wide range of marine organisms, in addition to fish, that live there. SSB researchers (Work Package 2) have investigated the scale of those biotic impacts and their biogeochemical consequences for scallop-dredging and otter-trawling in the Irish Sea. Their recently published7 results confirm that the magnitude of biogeochemical effects (e.g. for organic matter decomposition and nutrient cycling) depends on sediment grain size, being greater for muddy habitats than for sand. However, the hypothesis that such effects are primarily mediated through loss of benthic infauna and their bioturbation (biologically-driven sediment resuspension) was not supported. A complementary analysis relating fishing frequency to sediment organic carbon content and nutrient levels has been accepted for publication<.8

New insights on iron dynamics in shelf seas

Dissolved iron (dFe) is an essential micronutrient for marine life. Its abundance ‒ or lack of it ‒ is known to be closely linked with oxygen levels, with high dFe concentrations generally limited to oxygen-depleted conditions. SSB researchers (Work Package 3) were therefore surprised to find relatively high levels of dFe in the well-oxygenated waters of the Celtic Sea during the 2014-15 ship-based fieldwork programme. The source of this dFe was seafloor sediments, with the oxidation of reduced iron (removing dFe by changing it to insoluble forms) occurring more slowly than expected9. High dFe waters were found to persist 10-30 m above the seafloor; they were also shown to be transported off the shelf in plumes containing fine particles of suspended material (nepheloid layers). Further analytical work on samples from these particle-rich layers has recently been conducted at the Diamond Light Source, the UK’s national synchrotron facility at Harwell. Close linkage with modellers in SSB Work Package 4 is greatly improving the representation of these and other features of iron dynamics in whole-ecosystem models for shelf seas, including new equations describing iron scavenging and bacterial iron uptake and remineralization.

Added value from combining experimental and modelling approaches

The representation of the decomposition of organic material in ocean ecosystem models is arguably as important as its creation, since it completes the natural cycle. Timescales are, however, crucially important – affecting spatial patterning of biohgeochemical interactions over a range of 3D scales and hence associated feedback processes. For example, the bacterial breakdown of dissolved organic nitrogen (DON) affects the availability of assimilable nitrate, and hence may limit ocean primary production. Joint work between SSB modellers (Work Package 4) and experimentalists investigated the timescales of DON breakdown by the marine bacterium Alteromonas sp: they found10 that this species – although considered to be metabolically versatile – was only able to degrade ~35% of phytoplankton-derived DON over a ~6 month period. In contrast, 75% of dissolved organic carbon (DOC) was used. These effects could be well-simulated by models, and therefore provide opportunities to improve both the generic and site-specific representation of nutrient cycles under current-day condition ‒ and also in projections of scenario-dependent future conditions.

Quantifying carbon storage in European shelf seas

Carbon dioxide levels in the atmosphere are influenced by ocean-based sources and sinks, as well as by emissions directly due to human activities. It is therefore important to know how much potentially-mobile carbon occurs in different parts of the marine environment area, its current stability/lability, and how that might change in future under different human management scenarios or climate regimes. Using new methods, SSB researchers (Work Packages 5 and 2) estimated11 the organic carbon content of the top 10 cm of sediment in the North-West European continental shelf to be ~ 434 million tonnes, for an area of 1.1 million km2. Contrary to expectations, most carbon was in coarse-grained sediments. The confidence limits for the estimate were, however, relatively large (230 – 882 Mt, 5th and 95th percentiles), with uncertainties relating to the processes affecting organic carbon storage and the likelihood of their spatial variability within the study.

August 2016

UK marine carbon storage – what’s it worth?

The Paris Agreement on climate change has increased the attention to the natural processes that remove carbon dioxide from the atmosphere on a longterm basis. On land, the scale of that removal and storage is relatively well-quantified, but we know much less about the equivalent processes in coastal areas and shelf seas. SSB researchers at Cefas and UEA have now estimated current UK ‘blue carbon’ storage to be around 220 million tonnes, with an accounting value of more than £5 billion12. A key consideration is the stability of the storage; i.e. the risk of losing carbon from marine sediments back to the atmosphere, as has already happened through the drainage and ‘reclamation’ of coastal wetlands. Thus an analysis of eight major European estuaries has indicated a ~40 fold decrease in their carbon storage as a result of human activities13. Part, but not all, of that decrease could be reversed, if managed retreat (allowing coastal flooding in some localities) were to become the main response to global sea level rise.

Novel techniques for tracking iron inputs to North Atlantic

Iron (Fe) is a crucial micro-nutrient in short supply in the open ocean, due to its poor solubility and removal by biological processes: it is therefore important to know how much is provided by input from shelf sea and shelf-slope sediments. Direct Fe measurements give data on concentrations but not lateral transport rates. SSB researchers at the Universities of Edinburgh and Southampton determined the latter by using the naturally-occurring radium isotope 224Ra, with a half-life of 3.66 days. Since it is known that the shelf sediments are the sources of both 224Ra and Fe, the rate of movement of the latter (also carbon and other elements) from the Celtic Sea to the North Atlantic can be determined. Fe delivery to the open ocean was found to be dominated by very small (colloidal) particles, with high temporal variability associated with sediment resuspension. Overall supply rates were higher than those determined using different, less sophisticated, approaches.

February 2016

A year and a half of fieldwork now yielding a wealth of results

After more than 200 days at sea, and involving more than 120 researchers, the last of nine Shelf Sea Biochemistry research cruises was successfully completed on 2nd September 2015. The cruise re-scheduling that occurred in 2014 had been seen as a problem; now it is considered to be a substantive ‘blessing in disguise’. Thus there has not only been a ~50% increase in the number of datasets collected (compared to what was originally planned), but a much greater increase in their scientific value - since temporal coverage was extended from 9 to 18 months, with replicate information for processes occurring in the key spring-summer period. The effort spent on data collection is now being directed at data analysis and interpretation, with initial outcomes presented at the second SSB Annual Science Workshop, held at Plymouth Marine Laboratory, 24-25 November. Particularly exciting outcomes included the high-resolution, glider-based studies of shelf edge processes (with linkage to the FASTNEt programme); novel information on extremely low iron levels in surface waters of the Celtic Sea (with the possibility that iron may be limiting productivity); evidence for important seasonal changes in phytoplankton biochemistry, (affecting their food quality for zooplankton); and initial analysis of a unique dataset on how trawling can affect sediment carbon storage.

July 2015

An ambitious field work programme now (nearly) completed

Four Shelf Sea Biochemistry (SSB) research cruises have been successfully completed so far this year, DY 021, DY 029, DY 030 and DY 033, and a fifth – concluding – cruise DY 034 is now underway. All have been investigating the interacting physical, chemical and biological processes in the Celtic Sea, in both the water column, the sediment and off the shelf edge, and have used RRS Discovery as the platform for deployment of a very wide range of instruments, sampling gear and autonomous devices. Fortunately there have been no recurrences of the winch problems that caused major set-backs in 2014, resulting in the re-scheduling of most of the work to 2015. But the cruise series has been challenging in other ways: in particular, Autosub was lost – but then re-located – on DY 021 (1-26 March), with subsequent recovery involving the Cefas vessel RV Endeavour. Despite that period when it was out of action, Autosub has provided more than 1200 seafloor images, giving semi-quantitative information on the distributions and abundances of ~100 species of benthic macrofauna. Such information will be combined with the wealth of other data obtained from the cruises, including near-unique detailed coverage of the development of the spring bloom – with interpretation enhanced by satellite data and instrumented moorings. Day-to-day coverage of the SSB cruises and their wide-ranging scientific activities have been provided by frequent blog posts

January 2015

Catching ‘snow’ in the Celtic Sea

The dynamic behaviour of organic aggregates and particles (marine ‘snow’) is of crucial importance to the recycling (and removal) of nutrients and carbon in the ocean. The NOC Snowcatcher has recently been developed to investigate such material, with several successful deep-water deployments, e.g. in the Southern Ocean and open Atlantic. The Snowcatcher comprises a cylindrical container to collect a relatively-undisturbed 400 litre sample of seawater, and the suspended particles it contains, from specified water depths. The settling rates, size distributions and chemical compositions of those particles can then be determined. This equipment was used for the first time in near-coastal waters on the Shelf Sea Biogeochemistry ‘trials and training’ cruise (Discovery 026, August 2014); subsequently it was one of the main sampling devices used on the SSB early-winter cruise (Discovery 018, November-December 2014),14 with focus on water column processes. Although there were teething problems with some of the modifications made to the Snowcatcher for its SSB use, those problems were overcome – and it provided samples and data that will greatly improve our understanding of bacterially-driven recycling processes. Contrary to expectations, very little time was lost to poor weather on the early winter cruise. Its Principle Scientist, Jonathan Sharples (Liverpool University) concluded that cruise DY 018 was “very productive, with remarkable weather allowing us to do a lot more than we expected”.

Near-complete seasonal coverage for shelf-wide CO2 survey

Not all the Shelf Sea Biogeochemistry field work is dependent on shiptime on RRS Discovery. Since April 2014, thousands of other seawater samples have also been collected by a wide range of research vessels, as part of the water column (pelagic) Work Package. This unique sampling covers an area around all the UK, from the northern North Sea to Rockall and the Bay of Biscay, and involves (in addition to NERC research vessels) ships from four organisations: Centre for Environment, Fisheries & Aquaculture Science (Cefas), Marine Scotland, the Agri-Food and Biosciences Institute (AFBI) and the Marine Institute in Ireland. Additional data are being collected by Ferryboxes - equipment that automatically analyses water samples - on ferries from Germany, Spain and Norway into UK waters. The main samples are collected at midday, filtered and frozen. Subsequently, they are analysed at NOC (in Southampton and Liverpool), the University of Liverpool and Plymouth Marine Laboratory, to determine the carbon and nutrient levels in the water and hence how much carbon dioxide (CO2) is being taken up by the ocean at different times of year. After 10 months, the seasonal cycle is now near complete; it is expected to continue the survey until October 2015, providing not only full annual coverage but also additional information on year-to-year variability. For further details, see the NOC online article15 issued as a press release.

July 2014

First SSB research cruise meets most objectives, despite problems

The ‘core science’ of the Shelf Sea Biogeochemistry programme has been constructed around ship-based studies in the Celtic Sea, between Cornwall, southern Ireland and the open Atlantic. A sequence of six research cruises, involving more than 150 days at sea, was planned on the new RRS Discovery between mid-March and early December 2014, to quantify key processes linking seasonal cycles in the water column and the seafloor. The first cruise (DY 008, 20 March – 13 April), focussed effort on the seafloor conditions prior to the main onset of biological activity (‘spring bloom’) in the overlying water, expected to occur in mid-late April. Led by Henry Ruhl (NOC Southampton), a multidisciplinary team from seven laboratories was able to: deploy landers, moorings and gliders; use Autosub 6000, multibeam and other techniques for site surveys; and carry out extensive coring and CTD sampling. The data and samples collected on DY 008 therefore provide an excellent starting point for subsequent studies. DY 008 was, however, the first science cruise on Discovery – and several ‘teething problems’ were encountered. The most serious of these related to winch operations, of crucial importance for gear deployment/ recovery and sample collection. Immediately prior to the cruise, additional trials and testing had been carried out, but not all issues could be resolved. An engineer from the winch manufacturers therefore joined DY 008; his diagnosis was that extensive further trials/testing were needed. As a result, it was reluctantly decided by the SSB Executive Board and National Marine Facilities to re-schedule the rest of the SSB cruise series.

The complexities of re-scheduling: now back on track?

The problems with the new RRS Discovery were not entirely unexpected, since the performance of her winches had given cause for concern earlier in the year. As a result, a risk management plan had been prepared, to assess options in the event of slippage of days or weeks at the start of the programme. That exercise showed that, in order to achieve the programme’s scientific objectives, significant slippage would require the main effort to be re-scheduled to 2015, although some work in late 2014 would also be of value. During April-June 2014, the full implications of the non-availability of Discovery were carefully considered by the SSB management team, including Work Package leaders, with wider input from the community. Revised costings were required for most awards and their components, since extensions to the contracts of most researchers were necessary to take account of the re-scheduling. Fortunately NERC was able to provide financial supplementation to the programme as a whole, to cover such additional costs. It has also been possible to continue with a scaled-down fieldwork programme during 2014, for servicing of the moorings and landers deployed from DY 008 in March. Furthermore, an additional cruise (DY 026) has been arranged in August 2014, in order to provide a platform for data-collection by SSB research students and an ‘added value’ science project. The latter, led by Richard Sanders (NOC Southampton) includes protocol development for the marine snowcatcher, a sampling device to collect sinking or re-suspended particles in the water column. There is now cautious optimism that Discovery will be able to provide the necessary winch capabilities during DY 026 – and that there will be overall science benefits by having data and samples from both 2014 and 2015.

January 2014

New programme component to quantify ‘blue carbon’ dynamics

How important are UK seas in absorbing CO2 from the atmosphere, and keeping it out of circulation? Will that ecosystem service increase or decrease in future? Those questions will be addressed by a major new component added to the Shelf Sea Biogeochemistry programme in late 2013, as a joint award to Cefas Lowestoft, the University of East Anglia, the Met Office and many other partners. Such work will build on other parts of the programme, directly investigating CO2 exchanges at the sea surface, and carbon dynamics in the water column and sediment. The blue carbon component will also assess the role of human activities in changing such processes. For example, does sea bed disturbance (trawling, dredging, renewable placements) or coastal management actions (e.g. to reduce flood risk) have a significant effect on longterm carbon storage? At present, national greenhouse gas accounting includes estimates for land-based sources and sinks (from industry, forestry and agriculture) but does not take account of the equivalent processes occurring in national marine waters. Whilst the scale of such fluxes may prove too uncertain for ‘carbon credits’, best estimates of their current and future magnitude are urgently needed to improve policy responses to projected climate change. This topic area is therefore of interest to several government departments, and Defra co-funding enabled its inclusion in the SSB programme.

Planning (near-) completed for ambitious research cruise series

For marine research, programmatic structure and scaling make it possible to collect much more comprehensive (and therefore valuable) datasets than separate single-project studies. In particular, the multidisciplinary framework of the Shelf Sea Biogeochemistry programme, involving a very wide suite of process measurements, has been designed to deliver substantive improvements in ‘whole ecosystem’ marine models – linking physics, chemistry and biology; coastal waters, shelf seas and the open ocean; and the water column and sea-floor sediments. The detailed planning for such fieldwork has now mostly been completed, to be based on six research cruises (with more than 150 days at sea) on the new RRS Discovery, between mid-March and early December 2014. More than 100 researchers are involved, from around 15 UK research groups, centres and laboratories. The geographical focus for such effort is the Celtic Sea, between Cornwall and southern Ireland; there are important fisheries in that region, and processes occurring there can affect much larger areas. The scaling-up will be assisted by survey data collected on other ships, with collaborations involving Ireland, France, Spain, Germany, Denmark and Norway. The first SSB Annual Science Meeting (Liverpool, 15-17 January 2014) brought together the different teams within the programme to finalise fieldwork plans, maximising their benefit for the modelling groups.

Stakeholder linkages focus on Good Environmental Status and how that might be achieved

The Celtic Seas Partnership is an EU-funded, NGO-led activity, directed at improving the sustainability of marine resource use in the Celtic Seas (from NW Scotland to Brittany, including the western Channel). NERC is involved as a partner, with engagement through the British Oceanographic Data Centre and the Shelf Sea Biogeochemistry programme. Mutual advantage is thereby obtained: CSP is linked to strategic research and marine data sources, whilst the SSB programme has ready access to a network of stakeholders, mostly non-governmental, with interests in marine environmental issues. Initial liaison has focussed on how Good Environmental Status (as defined by the EU Marine Strategy Framework Directive) for the Celtic Seas might best be achieved, through integrated coastal zone management; the associated development of approaches based on ecosystem services; and the involvement of the very many groups, bodies and individuals involved in marine resource use and management. In the past six months, CSP representatives have participated in the SSB launch meeting (Southampton, October 2013) and the first Annual Science Meeting (Liverpool, January 2014), whilst SSB researchers have played an active role in two CSP workshops on the topic of Good Environmental Status (both in Liverpool, October 2013 and January 2014). The scheduling of the second CSP workshop and the SSB ASM was deliberately complementary.


Notes

  1. Birchill AJ et al. (2017) Geophysical Research Letters; online (doi: 10.2002/20217GL073881)
  2. Presentation at Challenger Society’s Advances in Marine Biogeochemistry conference (AMBIO VIII), Oban, 6-7 Sept. Ten other presentations (6 oral, 4 poster) at this meeting were based on results from the SSB programme
  3. https://link.springer.com/journal/10533/135/1/page/1  
  4. Solan et al (2017); http://www.ingentaconnect.com/content/sil/impact/2017/00002017/00000007/art00005
  5. Abstracts online via http://adsabs.harvard.edu/abs/2017EGUGA
  6. Sharples J, Middelburg JJ, Fennel K & Jickells TD (2016) What proportion of riverine nutrients reaches the open ocean? Global Biogeochemical Cycles 31; doi: 10.10002/2016GB005483.  [Paper given Research Spotlight status by AGU: https://eos.org/research-spotlights/what-proportion-of-river-nutrients-reaches-the-open-sea]
  7. Sciberras M, Parker R, Powell C, Robertson C, Kröger S, Bolam S, Hiddink JG (2016) Impacts of bottom fishing on the sediment infaunal community and biogeochemistry of cohesive and non-cohesive sediments.  Limnology & Oceanography 61, 2076-2089; doi; 10.1002/lno.10354.
  8. Hale R, Godbold JA, Sciberras M, Dwight J, Wood CL, Hiddink J & Solan M (2017) Mediation of macronutrients and carbon by post-disturbance shelf sea sediment communities. Biogeochemistry (in press).
  9. Klar JK, Homoky WB, Statham PJ, Birchill AJ, Harris E, Woodward EMS, Silburn B, Cooper M, James RH, Connelly DP, Chever F, Lichtschlag A & Graves C (2017) Stability of dissolved and soluble Fe(II) in shelf sediment pore waters and release to an oxic water column. Biogeochemistry (in press)
  10. Polimene L, Clark D, Kimmance S & McCormack P (2017) A substantial fraction of phytoplankton-derived DON is resistant to degradation by a metabolically versatile, widely distributed marine bacterium. PLoS ONE 12, e0171391; doi: 10.1371/journal.pone.0171391
  11. Diesing M, Kröger S, Parker R, Jenkins C, Mason C & Weston K (2017) Predicting the standing stock of organic carbon in surface sediments of the North-West European continental shelf.  Biogeochemistry (online); doi: 10.1007/s10533-017-0310-4
  12. Submission to Nature Climate Change.  Quoted values should not be more widely disseminated until formally published.
  13. Jickells TD, Andrews JE & Parkes DJ (2016) Direct and indirect effects of estuarine reclamation on nutrient and metal fluxes in the global coastal zone. Aquatic Geochemistry. 22, 337-348; doi: 10.1007/s10498-015-9278-7
  14. Cruise blog at https://jonathanatsea.wordpress.com; information on Snowcatcher deployments given in entries for 12, 13, 19, 24 and 30 November.
  15. “Frozen sea samples link climate, chemistry and carbon” posted 21 November http://noc.ac.uk/news/frozen-sea-samples-link-climate-chemistry-carbon