Expedition Luymes Bank

On 18 December, the team arrived back in Guadaloupe after a fantastic week and a half of exploring the Luymes Bank.They made some amazing discoveries in the world's largest and deepest sinkholes. A lot of research work to be done back home!

DROWNED SINKHOLES

During NICO cruises in 2018 drowned sinkholes were discovered in the Saba Bank. They occur in the NW corner of the Saba Bank, a drowned peninsula at ca 80m depth called the Luymes Bank. Altogether more than twenty sinkholes were identified based on bathymetry. Diameters of sinkholes varied from 70 to 1100 m and depths varied between 10-300m. The discovered sinkholes in the Saba Bank comprise the largest sinkholes ever found world-wide (Meesters pers comm ).

In one of two sinkholes explored with camera’s, peculiar pillar-like calcium carbonate accretions were found with diameters of 40-60cm and protruding up to 1m from the sandy bottom. Pillars were found to stand neatly ordered on the bottom at a depth of 120 m. Based on the pink color on top, pillars look like features formed by crustose coralline algae of unusual size and density, almost in a stromatolitic fashion. The proposed research plans to investigate the environmental conditions in various sinkholes to understand why some sinkholes harbor these pillars and others do not. Trophic conditions (including inorganic nutrients) and water exchange between sinkholes and overlying water will be determined. Moreover pillars will be investigated in more detail to assess the species consortia producing these pillars, their life history strategies, accretion rates and down-core history. Carbonate chemistry in sinkholes will be addressed to assess the conditions under which these pillars accrete (high-Mg calcite in coralline rhodophytes).

EXPEDITION

From 5 to 20 December, the Royal Netherlands Institute for Sea Research (NIOZ) and Wageningen Marine Research are organising an expedition to the Saba Bank, close to the Dutch island of Saba in the Caribbean region. Experts on board the research vessel Pelagia hope to acquire more knowledge about the sinkholes and the hundreds of recently discovered strange calcareous algae turrets.

The researchers will extensively explore all 21 sinkholes on the Saba Bank. The aim is to find out more about the nature of the calcareous algae turrets and the environmental factors that influence their growth. How does the exchange of water between the sinkholes and the flowing water above work, and which biological communities and nutrients such as bacteria are present? This research will provide insights into why these turrets occur at some sinkholes but not others.

The research vessel will drop a wide range of measurement equipment and cameras to a depth of many tens of metres. These will be used to collect various data about the water column, and take samples of water and seafloor life, including an effort to bring several turrets to the surface. The researchers will also place anchors with measurement equipment in the sinkholes so that about seven days of monitoring will be possible during the expedition.