{"id":68,"date":"2026-06-22T09:00:37","date_gmt":"2026-06-22T08:00:37","guid":{"rendered":"https:\/\/www.oceanblogs.org\/m219\/?p=68"},"modified":"2026-06-22T09:00:41","modified_gmt":"2026-06-22T08:00:41","slug":"what-can-pies-tell-us-about-the-current-system","status":"publish","type":"post","link":"https:\/\/www.oceanblogs.org\/m219\/2026\/06\/22\/what-can-pies-tell-us-about-the-current-system\/","title":{"rendered":"What can PIES tell us about the current system?"},"content":{"rendered":"\n

By Tina Hans (GEOMAR)<\/p>\n\n\n\n

One main objective of the cruise is to investigate the large-scale ocean currents in the tropical Atlantic. For that purpose, we are maintaining several long-term observatories at the seafloor and in the water column. Additional to the moorings which have been described in the previous blog \u201cKeeping the record alive\u201d, we deployed and recovered close to the Brazilian coast so-called PIES. They have \u2013 as some might say unfortunately \u2013 nothing to do with pastries but are oceanographic instruments that measure the pressure at the seafloor as well as the time an acoustic signal takes to travel from the instrument to surface, where the signal is reflected, and back. We deployed six of those instruments across the continental shelf off Brazil at depth ranging from 150 metres to 3000 metres. These deployments are the result of a collaboration with the University of Bremen. We also successfully recovered one PIES that spent just over three years at the seafloor at a depth of 500 metres. With the data of the recovered PIES, we could extend our time series of seafloor pressure measurements at 500 metres depth. This time series, which goes back until 2013, spans now 13 years.<\/p>\n\n\n\n

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Pictures of a PIES deployment (left), a recovered PIES (upper right), and a PIES ready for deployment (lower right). Photos taken by Leonie Jaeger, Mario M\u00fcller, and Naomi Krauzig.<\/em><\/figcaption><\/figure>\n\n\n\n

This still leaves the question of what the pressure at the seafloor can tell us about ocean currents. To answer this, one needs to know that the ocean dynamics are largely governed by a balance of two physical forces: the pressure gradient force and the Coriolis force. Essentially, when water \u2018piles up\u2019 somewhere, a current is created which attempts to even out the differences, and the direction of this current is deflected due to the Earth\u2019s rotation. This force balance can also be used to directly relate the difference in pressure between two locations to the mean velocity in between these locations. We make use of this relation by measuring the seafloor pressure not just off Brazil but also off Angola at a similar latitude. With the combination of these measurements, we can calculate the mean north-\/southward velocities across the Atlantic between Brazil and Angola. From this velocity we can then derive the strength of the Atlantic Meridional Overturning Circulation (AMOC).<\/p>\n\n\n\n

However, there is one caveat: the pressure sensors are drifting over time. This makes it impossible to make statements about long-term trends, but we can still make statements about the seasonal to interannual variability of the AMOC. Therefore, the measurements of the PIES can be used to better understand the large-scale currents in the tropical Atlantic. In a next step, we are now using these measurements to better understand the linkage of the AMOC to climate variability in the tropics.<\/p>\n\n\n\n

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Time series of seafloor pressure at 500 metres depth at the continental shelf off Brazil. The different colours indicate the different instruments which have been deployed since 2013. The measurements of the PIES that was recovered during this cruise is coloured in green. The black line shows monthly mean values. Pressure changes can be induced by changes in the water level (a change of 0.05 decibar roughly corresponds to 5 centimetres) or by changes in the temperature and salinity characteristics of the water column above the instrument. When looking at the time series, distinct seasonal and interannual variability is apparent. No long-term variability is visible as this is removed with removing the instrumental drift.<\/em><\/figcaption><\/figure>\n","protected":false},"excerpt":{"rendered":"

By Tina Hans (GEOMAR) One main objective of the cruise is to investigate the large-scale ocean currents in the tropical Atlantic. For that purpose, we are maintaining several long-term observatories at the seafloor and in the water column. Additional to the moorings which have been described in the previous blog \u201cKeeping the record alive\u201d, we […]<\/p>\n","protected":false},"author":272,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[7],"tags":[],"class_list":["post-68","post","type-post","status-publish","format-standard","hentry","category-at-sea"],"_links":{"self":[{"href":"https:\/\/www.oceanblogs.org\/m219\/wp-json\/wp\/v2\/posts\/68","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.oceanblogs.org\/m219\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.oceanblogs.org\/m219\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.oceanblogs.org\/m219\/wp-json\/wp\/v2\/users\/272"}],"replies":[{"embeddable":true,"href":"https:\/\/www.oceanblogs.org\/m219\/wp-json\/wp\/v2\/comments?post=68"}],"version-history":[{"count":1,"href":"https:\/\/www.oceanblogs.org\/m219\/wp-json\/wp\/v2\/posts\/68\/revisions"}],"predecessor-version":[{"id":72,"href":"https:\/\/www.oceanblogs.org\/m219\/wp-json\/wp\/v2\/posts\/68\/revisions\/72"}],"wp:attachment":[{"href":"https:\/\/www.oceanblogs.org\/m219\/wp-json\/wp\/v2\/media?parent=68"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.oceanblogs.org\/m219\/wp-json\/wp\/v2\/categories?post=68"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.oceanblogs.org\/m219\/wp-json\/wp\/v2\/tags?post=68"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}