Shelf Sea Biogeochemistry blog

Showing posts with label nutrient cycle. Show all posts
Showing posts with label nutrient cycle. Show all posts

Tuesday 21 April 2015

Game of Filters: A Song of Filters and Water

Clare Davis and Calum Preece, University of Liverpool (Westeros)

The University of Liverpool team (picture 1) is responsible for determining the composition and relative concentrations of dissolved and particulate organic nutrients, namely carbon, nitrogen and phosphorus. This is a key part of understanding both nutrient cycling and the fate of carbon fixed by primary production in the shelf system.  

Picture 1. The Liverpool team with [Jon] Snow Catcher enjoying some afternoon sunshine. Photo: Jose Lozano.

In real terms, this equates to an awful lot of filtering during the SSB cruises. To achieve this we travel down from Filterfell in the North to Southampton where we join the ship. From then on, we employ all of the Seven Filtrations to collect a wide range of samples. But first of all, we trot our little legs over to whichever device we are using for sampling that day, be it Jon Snow Catcher, CTD or Ned SAPS, armed with Tygon Lannister tubing and fill our bottles with as much seawater as we can get our hands on. There is one exception however, when we are working alongside the Fe Island team we aren’t trusted in the clean lab so they sample their fancy CTD on our behalf and deliver the water to us.

During transects and at designated stations we collect water samples from the CTD which we analyse for dissolved organic nutrients, including dissolved organic phosphorus (DOP), dissolved organic nitrogen (DON), dissolved organic carbon (DOC), amino acids (AA) and coloured dissolved organic matter (CDOM). We define these nutrients as those which pass through what is arguably the king of filters; King GFFrey with a pore size of 0.7μm.

We collect a selfish amount of water from the CTD for sampling particulate nutrients, including particulate carbon, nitrogen, phosphorus, lipids, amino acids, stable nitrogen isotopes and pigments. We define the particulate fraction as anything stuck to King GFFrey after filtering a couple of litres of seawater (picture 2).  We also collect particulate samples from the now infamous Jon Snow Catcher. 

Picture 2. A [King] GFF[rey] filter covered with particulate material. Photo: Chata Seguro.

A personal favourite for sampling particulate nutrients is the honourable and reliable Ned SAPS. With the help of Lord Commander Jon Short (picture 3), his Men of the NMF Watch, and good old Ned SAPS we can filter hundreds of litres of seawater in situ, separating out large particles from smaller ones which can give us useful insight into the composition and variability of the different sized particles in the water column.

Picture 3. [Lord Commander] Jon Short of the NMF [Watch] and good old [Ned] SAPS. Photo: Chata Seguro.
After all the samples have been filtered most are frozen in the freezer room which lies beyond the great hangar, but the Cercei CDOM samples must be analysed on Hodor Horiba…Horiba before they degrade. This is helps us calibrate the CDOM sensors on Samuel ‘Tarly’ Ward’s sea gliders that roam the Celtic Sea.

While many are currently playing in the Game of Filters, there is no denying that the North is a force to be reckoned with as they rule over their Seven Filtration rigs across the not-so-narrow Celtic Sea.

The bloom is coming! And soon the seabed will be covered with marine snow…

Thursday 19 March 2015

Deployment of SPI camera to the ocan's seabed.

Louis Byrne, British Oceanographic Data Centre, NOC

Until Saturday when we are scheduled to depart to CANDYFLOSS we are finishing a spatial survey between the four benthic sites which we have been working at thus far. The work which we are doing at the four benthic stations helps us to understand how processes such as nutrient resuspension and carbon storage work in four different types of marine sediment (mud, sandy mud, muddy sand and sand). The purpose of the spatial survey is to put the data which we have been collecting at sites A, I, G and H into context and to look at gradients in sediment type between the main sites. To do this the program has created a network of 70 locations between the four sites. Our task is to sample as many as we can before we run out of time and head to CANDYFLOSS.

Image taken by a SPI camera

At each station we do two NIOZ cores and a SPI camera, which is an instrument that is lowered to the seabed and dropped into the sediment. It contains a prism to reflect the light 90 degrees so that when an image is taken by the camera, you get an image of the sediment and the overlying water. These images are then analysed to get an idea of the sediment type at that location and inspected for any signs of animal life.

Map of Celtic Sea showing four main benthic sites and CANDYFLOSS. Map created by Kirsty Morris (National Oceanography Centre, Southampton)

From the sediment samples brought up by the NIOZ cores, we can find out the sediment type at that particular location, and a variety of measurements are taken including organic carbon, nutrient and chlorophyll concentrations, as well as particle size, porosity (the space between the grains of the sediment) and the oxygen concentrations in the water between the grains of sediment.

Coring while performing the spatial survey

All of these measurements combined will give us a good idea of how carbon and nutrients are being cycled in the shelf seas over a wide area of the Celtic Sea, with the hope that these data can be extrapolated to cover all of the shelf seas around the UK and parts of continental Europe. This will then give us a much better understanding of the nutrient cycle in this area of the world, and we will be able to estimate how much carbon from the atmosphere is being stored in UK sediments.

Kirsty Morris operating the SPI camera just before it hits the seabed.