De­ci­pher­ing the in­tens­ity of past ocean cur­rents

In the 6x11 meter flume tank, an ar­ti­fi­cial con­tin­ental slope was re­cre­ated by hand. The cir­cu­lar photo shows first au­thor Hen­ri­ette Wil­ck­ens form­ing the slope from sed­i­ment. The wa­ter-filled tank can be seen in the back­ground.
Photo Mont­age Credit: MARUM – Cen­ter for Mar­ine En­vir­on­mental Sci­ences, Uni­versity of Bre­men, E. Mira­montes

Ocean cur­rents de­term­ine the struc­ture of the deep-sea ocean floor and the trans­port of sed­i­ments, or­ganic car­bon, nu­tri­ents and pol­lut­ants. In flume-tank ex­per­i­ments, re­search­ers from MARUM – Cen­ter for Mar­ine En­vir­on­mental Sci­ences at the Uni­versity of Bre­men have sim­u­lated how cur­rents shape the sea­floor and con­trol sed­i­ment de­pos­ition. This will help in re­con­struc­tions of past mar­ine con­di­tions. They have now pub­lished their res­ults in the Nature journal Communications Earth & Environment.

De­tails of past cli­mate con­di­tions are re­vealed to re­search­ers not only by sed­i­ment samples from the ocean floor, but also by the sur­face of the sea­floor, which is ex­posed to cur­rents that are con­stantly al­ter­ing it. De­pos­its shaped by near-bot­tom cur­rents are called con­tour­ites. These sed­i­ment de­pos­its con­tain in­form­a­tion about past ocean con­di­tions as well as clues to cli­mate. Con­tour­ites are of­ten found on con­tin­ental slopes or around deep-sea moun­tains. But they can be found in any en­vir­on­ment where strong cur­rents oc­cur near the sea­floor. The mech­an­isms that con­trol them are not yet well un­der­stood. Ex­per­i­ments in flume tanks will help to change this through the de­pic­tion of de­pos­ition in fu­ture mod­els.

Underwater image of the flume tank with current meter. On the left you can see the artificial continental slope at the beginning of the experiment, on the right at the end of the measurement. New structures (contourites) of sediment have formed due to the flow in the tank. If the current strength is changed, the shape of the contourites also changes.
Photo Credit: MARUM – Center for Marine Environmental Sciences, University of Bremen; H. Wilckens

Detailed observations of changes in flume-tank experiments

Hen­ri­ette Wil­ck­ens, first au­thor of the newly pub­lished study, cre­ated a rep­lica of the con­tin­ental slope in a spe­cial flume tank at the Uni­versity of Utrecht (Neth­er­lands). Cur­rents and sed­i­ment in­put in the flume tank were sim­u­lated us­ing pumps and mon­itored with a cur­rent meter. The form­a­tion and de­vel­op­ment of the sed­i­ment de­pos­its were meas­ured with a laser scan­ner. All the data ob­tained were com­pared to meas­ure­ments in nat­ural ocean sys­tems in or­der to val­id­ate the res­ults of the ex­per­i­ments.

“The in­ternal sed­i­ment ar­chi­tec­ture of con­tour­ites can be ob­served from seis­mic data, but in or­der to un­lock in­form­a­tion about the past ocean cur­rents we need a bet­ter un­der­stand­ing of how they de­veloped and the factors that in­flu­ence the con­tour­ite sys­tems,” ex­plains Wil­ck­ens. While it is im­possible to dir­ectly see how nat­ural mar­ine sys­tems that de­veloped over time peri­ods of thou­sands to mil­lions of years star­ted to form on the sea­floor, sci­ent­ists can em­ploy flume-tank ex­per­i­ments to dir­ectly ob­serve de­tailed changes of the sea­floor mor­pho­logy and con­trol their re­lated cur­rent ve­lo­cit­ies.

Huge application potential of the models

“Our ex­per­i­ment can also be ap­plied to the en­tire deep sea and even to lakes,” says Hen­ri­ette Wil­ck­ens, mean­ing any­where in the deep sea where there is a slope, ter­races, deep-sea moun­tains or, for ex­ample, cold-wa­ter coral mounds.

It is also con­ceiv­able that the mod­els could be ap­plied, for ex­ample, to im­prove pre­dic­tions of how cur­rents trans­port mi­cro­plastic particles or other pol­lut­ants in the ocean. “The po­ten­tial for its ap­plic­a­tion,” says Wil­ck­ens, “is im­mense. The sys­tem must first be un­der­stood be­fore it is pos­sible to de­rive in­form­a­tion from it.”

Opening a new branch of research

“This re­search work is an im­port­ant step to­ward a bet­ter un­der­stand­ing of the ways in which ocean cur­rents con­trol the de­pos­ition of particles in the sea­floor, which has im­port­ant im­plic­a­tions for palaeoceanographic re­con­struc­tions and benthic eco­logy. This in­tro­duces a new branch of re­search that will prob­ably lead to even more ex­cit­ing dis­cov­er­ies,” ac­cord­ing to Elda Mira­montes, co-au­thor of the study and head of the “Sed­i­mento­logy” work­ing group at MARUM.

Published in journal: Communications Earth & Environment

Source/Credit: MARUM – Center for Marine Environmental Sciences

Reference Number: es100923_02

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