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Abundance, distribution, and diving ecology

research by Syntia

Freediving with Nik Linder, world record holder in freediving under ice and dynamic apnea

Today I was honoured to step into a discussion with Bauer crew experts about the risks of ice diving and polar scientific research from their past expeditions.

Bauer Compressors, founded in Munich in 1946 is recognised as the world’s foremost innovative designer and manufacturer of high and low pressure systems, including air and gas treatment and measurement technology for all industrial applications. Bauer is the main supplier for the diving activities in Düsseldorf Boot 2023. The tower consists of slim steel struts and large acrylic glass surfaces, and has a capacity of 200,000 liters of water.

Bauer Compressors supports institutions in marine research with the provision of compressor systems and compressor maintenance, including the University of Rostock, marine biology research as part of the Polarstern missions, the research and media ship Aldebaran and the Australian NGO “Great Barrier Reef Legacy”, which researches coral death on the Great Barrier Reef.

Polarstern, Europe’s largest scientific vessel and icon of German polar research, is celebrating its fortieth anniversary since it started its first expeditions with polar research ships worldwide. It has carried out over 130 successful expeditions in the Arctic and Antarctic and has been a temporary home for thousands of researchers from Germany and around the world.

The use of new underwater technologies also plays a major role in planning the successor to the Polarstern. After the federal budget was passed in 2022, the BMBF enabled the AWI to start the Europe-wide tender for the construction of a new research icebreaker, scheduled to start the service in 2027. Polarstern is also intended to become an ambassador for sustainable shipbuilding and energy supply based on hybrid diesel-electric propulsion.

The energy of a closed system is steady until converted into other forms, such as when kinetic energy is transferred into thermal energy or vice versa, but it is never lost. However, this fundamental principle of natural science is often still a problem for climate research.

For example, in the case of the calculation of ocean currents, where small-scale vortices as well as mixing processes they induce need to be considered, without fully understanding where the energy for their creation originates from. Waves on a larger scale can disintegrate into small structures driving large movements. All these processes are important for the Earth’s climate and determine how temperatures will rise in the future.

Ex­ped­i­tion M180 SON­ETT (Syn­op­tic Obser­va­tions – a Nes­ted ap­proach to study Energy Trans­fer & Tur­bu­lence in the ocean) is a key part of the ocean ob­ser­va­tions in the second phase of TRR181 ‘En­ergy trans­fers in At­mo­sphere and Ocean’. The ex­ped­i­tion take sci­ent­ists to an ocean re­gion where they can ob­serve many pro­cesses that af­fect en­ergy fluxes in the ocean and the ocean’s ex­change with the at­mo­sphere.

Re­search­ers from MARUM – Cen­ter for Mar­ine and En­vir­on­mental Sci­ences at the Uni­versity of Bre­men, the Uni­versity of Bre­men, the Uni­versity of Ham­burg, the In­sti­tute for Baltic Sea Re­search Warnemünde (IOW) and the Helm­holtz Cen­ter Hereon are in­volved.

The work­ing area is loc­ated south­east of the Walvis Ridge in the east­ern South At­lantic. In this re­gion, the so-called Agul­has ed­dies, which are formed at the south­ern tip of Africa and mi­grate north­ward through the At­lantic, meet in­ternal tides gen­er­ated at the Walvis Ridge, and af­fect the propaga­tion of in­ternal tidal waves. The ed­dies form fronts and so-called fil­a­ments at their edges. Fil­a­ments are struc­tures that form where dif­fer­ent wa­ter masses meet. They look like elong­ated fin­gers on satel­lite im­ages. The planned ob­ser­va­tions in­clude sur­face fluxes and waves, sur­face layer pro­cesses, meso­scale and submeso­scale vari­ab­il­ity, ho­ri­zontal mix­ing, in­ternal wave en­ergy fluxes, the in­ter­ac­tion between in­ternal waves and ed­dies circular current, and the en­ergy dis­sip­a­tion in the ocean in­terior.

The ob­ser­va­tions will be com­ple­men­ted by runs of a high-res­ol­u­tion ocean cir­cu­la­tion model with tidal for­cing (ICON SMT-WAVE) from the Max Planck In­sti­tute for Met­eor­o­logy in Ham­burg, Ger­many, which will al­low to con­tex­tu­al­ize the ob­ser­va­tions, un­der­stand pro­cesses, and char­ac­ter­ize the en­ergy bal­ance of this ocean re­gion.

The ex­ped­i­tion started on Feb­ru­ary 23, 2022 in Mon­tevideo (Ur­uguay), on April 14 the team returned with MET­EOR in Cape Town (South Africa). Here, the re­search­ers re­ported life and work on board in a lo­g­book. Reference: https://www.marum.de/en/Discover/Logbuch-M180.html

Excerpts from the M180 SON­ETT logbook:
15 March 2022: A Drift­ing Pas­sen­ger
“On Wed­nes­day at the CTD sta­tion, we pulled up a catch: a worm-like an­imal out of the wa­ter. The semi-trans­par­ent tube looked al­most plastic and had in­ter­est­ing nubs of dif­fer­ent sizes grow­ing on its mantle. No one knew what we had unknowingly caught there. The first idea was that it could be a sea-cu­cum­ber. After a while, however, it was dis­covered that it was called a ”Pyro­some”, a colony con­sist­ing of sev­eral thou­sand in­di­vidual an­im­als. Because the individual tunicates can reproduce via cloning, the colony can regenerate injured parts or continue growing after being broken apart. Pyrosomes form an important biological substrate in the water column that other animals use for settlement.

Es­pe­cially dur­ing the night watches we no­ticed that these tu­nic­ates can of­ten be seen close to the wa­ter sur­face. Pyrosomes migrate up and down the water column daily to feed in the productive upper marine layers at night. At dusk, they migrate back to deeper water layers. During this migration, they actively transport their feces to these depths, while also releasing carbon through respiration.

Pyrosomes have an elongated shape with one open and one closed side. Credits: Nikos Lymperis

11 March 2022: Little Things, Big Im­pact
At­tached to the bot­tom of the ship and running con­stantly: the ves­sel- moun­ted ADCP fires pulses of sound down into the ocean and listens for any echoes com­ing back. Based on how long an echo takes to re­turn, and if the sound of it changed on the way, the speed and dir­ec­tion can be cal­cu­lated of wa­ter move­ments at dif­fer­ent depths be­low the ship. If any­thing other than the wa­ter re­turns an echo measures aren’t accurate.

Shortly after sunrise (yellow dashed line) a large gap in our signal grows around 300 metres depth then closes shortly after sunset (black dashed line). At the same time our strongest signals (anything above the dark line) move closer to the surface. This is due to the movement of plankton. Graph: Ryan Mole

By looking at the strength of the sig­nal a strange pat­tern emerges. Dur­ing the night, from down to 600 meters the echo be­comes too quiet to hear. Dur­ing the day, a gap in our sig­nal starts to emerge just after sun­rise and closes just after sun­set. The strength of our sig­nal in­creases near the sur­face whilst at the same time we get no echoes boun­cing back from deeper wa­ters, par­tic­u­larly around 300 meters.
Due to the move­ment of mi­cro­scopic plants and an­im­als known as plank­ton, which are al­most too small to see with the eye but are ex­cel­lent for boun­cing back an echo. Every day they mi­grate for hun­dreds of meters: to the sur­face 100 meters where there is light and they can feed and pho­to­syn­thes­ise by day, and down in deep wa­ter by night hide from pred­at­ors and get rid of waste. This mi­gra­tion hap­pens every day across much of the ocean and glob­ally is an im­port­ant route for get­ting nu­tri­ents and car­bon into deeper wa­ters.

Microorganisms in sea ice and the water column are cornerstones of this ecosystem and play critical roles in providing feedback to climate and maintaining food chains that are central to protection and ecosystem services. Due to their rapid adaptability to environment, marine microorganisms are biological indicators of the environment.

From Düsseldorf Boot 2023, the world’s largest water sports trade fair with 1,900 exhibitors from 60 countries, presenting their products and the most important awards for sailing and motor yachts in Europe.