Posts Tagged plankton

Antarctic Voyage: The biological pump – the importance of microscopic phytoplankton Guest Work Feb 27

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Writtenby  Helen Bostock (Marine Geologist, NIWA) and Elizabeth Shadwick (ACE CRC)

Date: 26/2/2013
Location: 65.111248°S, 146.056312°E
Weather: Sunny, less than 20 knots

Simplified Antarctic food web. [Courtney Derriman]

Sea state: 1-3 m swell

Phytoplankton are microscopic plants that live at the surface of the ocean.

There are billions of them in ocean surface waters, which are then grazed upon by millions of zooplankton (including krill), which are eaten by fish, which are eaten by bigger fish, which are eaten by seals and penguins (actually the Adelie penguins eat krill, just like the whales), which are eventually eaten by just a few top predators.

Thus, phytoplankton form the base of the marine food web.

Diatoms under a microscope – Odontella weissflogii, Corethron pennatum, Corethron sp., Asteromphlaus hookeri, Thalssiosira spp. [Leanne Armand, Macquarie University]

Phytoplankton photosynthesise, just like land plants, using sunlight to convert CO2 into organic carbon and oxygen (see blog post 13: The carbon team). The organic carbon is then used by the whole marine food web, and a small fraction of it eventually ends up in the deep ocean. This process of transferring carbon from the atmosphere to the deep ocean is called the biological pump.

As the sea ice melts back each summer in the Mertz Polynya, the surface waters are exposed to sunlight and there is an intense phytoplankton bloom. Due to the upwelling of nutrient-rich deep waters on to the shelf there is no shortage of nutrients (nitrate, phosphate, silicate) to feed this bloom.

The phytoplankton also need minor amounts of iron.  The iron is locally sourced from upwelling waters, dust (although this is minor in this region, it can be a major component in other areas of Antarctica) and coastal sediment.

Some of the resulting biomass then sinks to the sea floor. Thus during the brief Antarctic summer the biological pump is active in this region, transferring atmospheric CO2 to the deep ocean, via the formation of the Antarctic bottom water (see blog post 21: The formation of the Antarctic bottom water).

In the Southern Ocean and around Antarctica, the primary producers are diatoms. As well as organic carbon, these also produce a skeleton made out of silica. These silica skeletons are very intricate and beautiful under a microscope.

The filtering set up – the water is filtered through a 20mm, 5mm, 2mm and 0.45mm filter. [Courtney Derriman]

We have been filtering sea water to collect some of these diatoms (and other phytoplankton). We have also been deploying a plankton net – just like a fine meshed fishing net – to see if we can collect any zooplankton. The different species will be identified under a microscope to determine the abundance and changes in the diversity of the assemblage.

We will also use the filtered and towed plankton samples to test out some new geochemical proxies on the carbonate and silica skeletons. By comparing the geochemical values with modern environmental data (temperature, CO2, nutrients, salinity), we can produce a calibration. We can then analyse the geochemistry of the silica skeletons of the diatoms, which accumulate in the sediment cores, to interpret environmental changes over time (see blog posts 8: The geology team and coring and 22: Could the past be the key to the present).

So while plankton are not quite as photogenic as seals, penguins or whales – at least not with a regular camera as they require a high magnification microscope to view them – these creatures play an central role in the marine food web and global carbon cycle.

Ian Smith (crew) holding up the collection of plankton collected using the plankton net. [Courtney Derriman]

Antarctic Voyage: The Continuous Plankton Recorder Guest Work Feb 07

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Dr Helen Bostock, marine geologist at NIWA, writes:

Date: 6/2/2013
Position: 52.244066˚S, 164.093142˚E
Weather: Cloudy and getting cooler
Sea state: 1-2 m swell – not too rough

Yesterday, while many of us were in our beds trying to get over sea sickness, Mark Fenwick (the token biologist) and several of the crew deployed the Continuous Plankton Recorder (CPR), just south of Stewart Island.

The CPR (Diagram: Australian Antarctic Division)

The CPR is a rather ingenious contraption; it was first invented by Sir Alister Hardy in 1926 and used during the Discovery expedition to the Antarctic. The instrument – which is a metal box in the shape of a fish – was designed to be towed behind any ship at a water depth of about 10 m. Water passes into the CPR at the front, and plankton are filtered onto a slow-moving band of silk (270 micrometre mesh size) and covered by a second band of silk.

The silks and plankton are then spooled into a storage tank containing formalin (or formaldehyde) to preserve the plankton so they don’t rot. On return to the laboratory, the silk is removed from the mechanism and divided into samples representing 10 nautical miles (19 km) of tow. The plankton preserved in the silk are then identified and counted by specialist plankton taxonomists.

Map of known CPR tows. Credit: Southern Ocean Continuous Plankton Recorder Survey (SO-CPR)

The Southern Ocean Continuous Plankton Recorder Survey (SO-CPR) is an international program, currently involving Australia, Japan, Germany, and New Zealand, which has been running for a couple of decades. The CPR silks from this voyage will be sent to our colleagues at the Australian Antarctic Division in Hobart for analyses.

NIWA scientist Dr Julie Hall working with the CPR during the NZ IPY-CAML expedition. Credit: NIWA

The overall aim of the CPR surveys in this region is to map the biodiversity of the plankton. Plankton are at the top of the food chain in the oceans and thus any changes to their quantity and distribution will affect the higher organisms that live off them, such as fish and the whales.

Plankton also reproduce rapidly, are very abundant, and are sensitive to changes in environmental conditions. This means that they act as early warning indicators of the health of the Southern Ocean. It is much easier to sample for plankton than for whales! *

Most of the science crew are recovering from their sea sickness and are up and about today, ready for our first proper sampling station tomorrow – stay tuned!


* See the ‘Blue Whale News Blog’, which is chronicling the Amaltal Explorer’s current voyage looking for the world’s largest creature – the Antarctic blue whale. The 2013 Antarctic Blue Whale Voyage – or VWhale – departed from Nelson, New Zealand on board the MFV Amaltal Explorer on January 29, 2013.

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