Secrets in the sediments: What foraminifera reveal about the deep-sea

Expedition Log: These “popcorn” like organisms give us valuable insight into the development of the seafloor.

Published: 13.05.2026 Author: Celine Golda, Valerie Bellec, Christine Tømmervik Kollsgård, Daniel Hesjedal Wiberg

Popcorn-like shells and brown slime creatures under the microscope. — Surface sediment sample (sieved to 0,3 mm) showing foraminifera and sediment grains through the microscope. White snail-like particles show foraminifera, while black and clear particles are sand grains. Photo: Celine Golda, NGU.

On the first cruise of the year, while slowly moving away from the central axis of the Mohns ridge toward the western flank, we observe progressively thicker sediment cover blanketing the underlying bedrock.

These sediment blankets are often covered by both agglutinated and calcareous foraminifera (“forams”) which provide valuable insights into the sedimentary history and paleoclimate of deep-sea environments.

En stein på havbunnen med noen skjell på seg. — Caption 2: (a) Accumulation of agglutinated forams (dark brown colour), while white particles around the block show calcareous foraminifera. Lasers: 9 cm apart.Photo: MAREANO/Havforskningsinstituttet; taken by Ægir6000/NORMAR.

Blåaktige svampedyr og en reke er oppå en stein på havbunnen. — Photo 2 (b) Block/cobble covered by an encrusted sponge surrounded by calcareous foraminifera (small white dots). Photo: Ægir6000/NORMAR Photo: MAREANO/Havforskningsinstituttet; taken by Ægir6000/NORMAR.

Foraminifera are single celled eukaryotes that possess shells composed of organic, agglutinated, or calcareous materials which may consist of one or more chambers and are abundant in both modern and ancient marine environments. They have been estimated to include a minimum of 38 000 living and fossil species (Jones, 2013; Pawlowski, 2009) and are classified into two groups: benthic (sediment dwelling) and planktonic (water column dwelling).

For a better understanding of the sedimentation rate and the sedimentary history, MAREANO uses Pb-210 dating to obtain a chronological profile of the uppermost sediments. In deep-sea sediments, where sedimentation rates are typically low; Pb-210 dating alone may limit the temporal resolution of the sediment age profiles as it is widely used to determine ages in the past 100-150 years. Radiocarbon (14C) dating may bridge the chronological gap in deeper, older sediments where Pb-210 has decayed providing a longer and more continuous chronological profile. Upon arrival back at NGU, the sediment samples are freeze-dried, sieved and individual foram species are handpicked for radiocarbon dating. Suitable species, among others include the planktonic foraminifera Neogloboquadrina pachyderma.

We look forward to uncovering the paleoclimatic secrets preserved in the forams and in unlocking a long-term timeline of deep-sea sedimentation, allowing us to piece together past ocean conditions along the Mohns Ridge.