GeoLog

Southern Ocean

Imaggeo on Mondays: Monitoring Antarctica’s ocean current

Imaggeo on Mondays: Monitoring Antarctica’s ocean current

This week’s featured image depicts a quiet and still oceanic landscape in Antarctica, but polar scientists are studying how energetic and variable the ocean currents in this part of the world can be.

In this picture, the marine research vessel RRS James Clark Ross is making its way through the Lemaire Channel, a small passage off the coast of the Antarctic Peninsula, south of the southernmost tip of Chile. This channel is about 11 kilometres long and just 1,600 metres wide at its narrowest point, bordered by a spectacular range of steep cliffs.

At the time this photo was taken, the ship was headed to the Rothera Research Station, a British Antarctic Survey base on the white continent’s peninsula. The scientists aboard the vessel are part of a decades-long research campaign surveying the ocean current surrounding Antarctica, known as the Antarctic Circumpolar Current (ACC). The ACC is the world’s strongest and most influential current, transporting 165 million to 182 million cubic metres of water every second and connecting most of Earth’s major oceans. As such, any changes to the ACC have the potential to impact other marine environments around the world.

For more than 25 years, scientists from the UK’s National Oceanography Centre (NOC) have ventured south each Antarctic summer to measure the ocean’s physical features in one region of the Southern Ocean, called the Drake Passage. Spanning just 800 kilometres between the Falkland Islands and the Antarctic Peninsula, the Drake Passage is the shortest crossing from Antarctica to any other landmass. This makes it a prime spot to survey the ocean’s currents, as the flow is constricted to a narrow geographical region.

So far, researchers have completed 24 survey trips across the passage. The data collected during these trips have been used to assess how physical features of the ACC change, both throughout a single year and over the course of several years. Yvonne Firing at NOC leads the latest expeditions as part of the UK funded ORCHESTRA project. The continuation of this monitoring is helping scientists study how the ocean stores excess heat and carbon. No other ocean basin has been monitored so consistently, making the Drake Passage the most comprehensively studied part of the Southern Ocean.

By Olivia Trani, EGU Communications Officer

Imaggeo is the EGU’s online open access geosciences image repository. All geoscientists (and others) can submit their photographs and videos to this repository and, since it is open access, these images can be used for free by scientists for their presentations or publications, by educators and the general public, and some images can even be used freely for commercial purposes. Photographers also retain full rights of use, as Imaggeo images are licensed and distributed by the EGU under a Creative Commons licence. Submit your photos at http://imaggeo.egu.eu/upload/.

Imaggeo on Mondays: Crowned elephant seals do citizen science

Imaggeo on Mondays: Crowned elephant seals do citizen science

In the Southern Ocean and North Pacific lives a peculiar type of elephant seal. This group acts like any other marine mammal; they dive deep into the ocean, chow down on fish, and sunbathe on the beach. However, they do all this with scientific instruments attached to their heads. While the seals carry out their usual activities, the devices collect important oceanographic data that help scientists better understand our marine environment.

The practice of tagging elephant seals to obtain data started in 2004, and today equipped seals are the largest contributors of temperature and salinity profiles below of the 60th parallel south. You can find all sorts of data that has been collected by instrumented sea creatures through the Marine Mammals Exploring the Oceans Pole to Pole database online.

The female elephant seal, pictured here at Point Suzanne on the eastern end of the Kerguelen Islands in the Southern Ocean, is a member of this unusual headgear-wearing cohort. This particular seal had been roaming the sea for several months with the device (also known as a miniature Conductivity-Temperature-Depth sensor) on her head. As the seal dove hundreds of metres below the sea surface, the instrument captured the vertical profile of the area, recording the ocean’s temperature and salinity, as well as chlorophyll a fluorescence and concentrations. When the seal resurfaced, the sensor sent the data it had accrued to scientists by satellite.

Etienne Pauthenet, a PhD student at Stockholm University who was involved in a seal tagging campaign, had a chance to snap this photo before tranquilising the seal and retrieving the tag.

Using elephant seals and other marine mammals to collect data gives scientists the opportunity to analyse remote regions of the ocean that aren’t very accessible by vehicles. Studying these parts of the world are important for gaining insight on how oceans and their inhabitants are responding to climate change, for example. With the help of data-gathering elephant seals, researchers are able to amass in situ measurements from regions that previously had been hard to reach, apply this data to oceanographic models, and make predictions on ocean climate processes.

While gathering data via elephant seals are crucial to oceanographic research, Pauthenet explains that the practice is sometimes quite difficult. “It can be complicated to find back the seal, because of the Argo satellite signal precision. The quality of the signal depends on the position of the seal, if she is lying on her back for example, or if she is still in the water.”

While on the research campaign, Pauthenet and his colleagues were stationed at a small cabin on the shore of Point Suzanne and they walked the shore every day in search of the seal, relying on location points transmitted from a VHF radio. After seven days they finally located her and removed her valuable crown. The seal was then free to go about her business, having given her contribution to the hundreds of thousands of vertical profiles collected by marine mammal citizen scientists.

by Olivia Trani, EGU Communications Officer
Imaggeo is the EGU’s online open access geosciences image repository. All geoscientists (and others) can submit their photographs and videos to this repository and, since it is open access, these images can be used for free by scientists for their presentations or publications, by educators and the general public, and some images can even be used freely for commercial purposes. Photographers also retain full rights of use, as Imaggeo images are licensed and distributed by the EGU under a Creative Commons licence. Submit your photos at http://imaggeo.egu.eu/upload/.

Imaggeo on Mondays: A spectacular rainbow

Imaggeo on Mondays: A spectacular rainbow

Back in February 2005, François Dulac and Rémi Losno worked in the field in the very remote Kerguelen Islands (also known as the Desolation Islands). Located in the southern Indian Ocean they are one, of the two, only exposed parts of the mostly submerged Kerguelen Plateau.

Our work consisted in sampling atmospheric aerosols and their deposition by rain on the island, which is a meeting point for the roaring fourties (strong westerly winds found in the Southern Hemisphere between 40 and 50 degrees latitude) and the equally turbulent furious fifties (which occur at more southerly latitudes still).

The aim of the study was to evaluate the input of chemical elements (in very low concentrations) derived from continental soil dust, to the remote surface waters of the Southern Ocean. Given the scarcity of land areas at this latitude, the particles were expected to have travelled long distances before arriving at Kerguelen.

For example, iron – one of the major elements in the Earth crust and soils – is of particular interest in this oceanic area because it is a micro-nutrient that limits the productivity (and related CO2 sink) of the Southern Ocean.

The island’s air was often very clear and the horizontal visibility unusually high, as can be seen in the photo. It highlights that atmospheric aerosol concentrations (the mixture of solid and liquid particles from natural and anthropogenic sources) are very low in this environment. Field sampling and subsequent chemical analyses require constraining protocols adapted to ultra-traces in order to minimize contamination of samples and blank levels.

The unique atmospheric conditions also meant we had problems estimating distances: we often found ourselves underestimating the stretch between two points during our long walks between the base and our remote sampling stations. In addition, the combination of very clean air, low sun and fast running atmospheric low-pressure systems carrying water clouds at low-level over the cold ocean make rainbows relatively frequent.

Walking back to the base after changing samples, we were caught in a rain shower. Raindrops were almost falling horizontally due to the high wind speed, leaving the soil dry downwind of the stones and rocks lying on the ground. A few minutes later clouds had passed and sunlight reflecting and diffracting in the cloud droplets offered us a spectacular semi-circular rainbow.

It was particularly special because it displayed an infrequent combination of (i) the main, classic, bright rainbow that shows up at 138-140 degrees from the direction of the sunlight, (ii) a secondary rainbow due to double reflection of sunlight in droplets that appears higher on the horizon at an angle of about 127-130 degrees and with an inversion of colours compared to the main bow (red inside), and (iii) one supernumerary rainbow with pastel green, pink and purple fringes on the inner side of the primary bow.

This stacked rainbow is caused by interferences and was first explained in 1804 by Thomas Young. It indicates the presence of small, uniformly sized droplets.  The dark area visible here on the right-hand side between the primary and secondary rainbows is called the Alexander’s band, after the ancient Greek philosopher Alexander of Aphrodisias comments on Aristotle’s Meteorology treatise, published in the early 3rd century. It is due to a lack of light resulting from the fact that diffracted rays are either reflected back inside the primary rainbow (causing this area to be brighter) or outside the secondary rainbow.

By François Dulac, Laboratoire des Sciences du Climat et de l’EnvironnementCEA/LSCE, Gif-sur-Yvette, France

Imaggeo is the EGU’s online open access geosciences image repository. All geoscientists (and others) can submit their photographs and videos to this repository and, since it is open access, these images can be used for free by scientists for their presentations or publications, by educators and the general public, and some images can even be used freely for commercial purposes. Photographers also retain full rights of use, as Imaggeo images are licensed and distributed by the EGU under a Creative Commons licence. Submit your photos at http://imaggeo.egu.eu/upload/.

Imaggeo on Mondays: A feast of pancakes

The thought of pancake ice always makes me a little hungry – I just can’t help thinking about stacks of syrup-drowned pancakes, or crepes covered wish sugar and doused with lemon juice – but the science of pancake ice is quite a tempting topic too!

Pancake ice occurs in areas where ice formation is repeatedly disturbed by water movement. In the Southern Ocean, the water extremely open and the swell of the waves causes a large soupy mixture of saltwater and needle-like ice crystals (frazil) to form. This slushy mixture is known as grease ice. Cyclical movement of the slush causes crystals to be compressed and begin to form cakes. Over time, the ice crystals stick together to form thin pancakes that are roughly 30 centimetres to 3 metres in diameter, like these:

Pancake ice in Drake Passage, the Southern Ocean by Kenneth Mankoff. This photo is distributed by the EGU under a Creative Commons licence.

Pancake ice in Drake Passage, the Southern Ocean” by Kenneth Mankoff. This photo is distributed by the EGU under a Creative Commons licence.

This field of ice pancakes in the Southern Ocean is constantly moving as waves cause them to jostle and bump on the water’s surface. The bumping causes the soupy grease ice to be sloshed up onto the edges of each pancake. As the water drains away, a raised lip of ice crystals is left behind – the feature that gives pancake ice its wonderful pancake-like texture.

In the Northern Hemisphere, pancake ice may become more common as the decline in inter-annual sea ice cover frees up larger expanses of water and allows it to swell. Pancake ice isn’t exclusive to the oceans though – it can also form on rivers when temperatures are close to freezing point – enough to form ice crystals, but not so low that the whole river freezes over.

By Sara Mynott, EGU Communications Officer

References:

Linder, C. A.: Sea Ice Glossary. Woods Hole Oceanographic Institution, 2003 (accessed November 2013)

Wadhams, P.: How Does Arctic Sea Ice Form and Decay? NOAA, 2003 (accessed November 2013)

Wilkinson, J. P., DeCarolis, G. Ehlert, I et al.: Ice Tank Experiments Highlight Changes in Sea Ice Types, EOS Transactions, American Geophysical Union, 90, 81-82, 2009

The EGU’s open access geoscience image repository has a new and improved home at http://imaggeo.egu.eu! We’ve redesigned the website to give the database a more modern, image-based layout and have implemented a fully responsive page design. This means the new website adapts to the visitor’s screen size and looks good whether you’re using a smartphone, tablet or laptop.

Photos uploaded to Imaggeo are licensed under Creative Commons, meaning they can be used by scientists, the public, and even the press, provided the original author is credited. Further, you can now choose how you would like to licence your work. Users can also connect to Imaggeo through their social media accounts too! Find out more about the relaunch on the EGU website.