NIOZ-UU project: The impact of atmospheric noise on the Atlantic Meridional Overturning Circulation

Started in 2021 together with dr. Claudia Wieners at Utrecht University. We often talk about long term climate trends in ocean circulation, but there is also large day-to-day variability in ocean currents. Some of this variability comes from the atmosphere, short but strong weather events that last only a few days can force a response in the ocean. An example is the Greenland Tip Jet, a strong westerly wind that occurs at the southern tip of Greenland several times each winter. In this project we recreate these wind events in an idealized setting of a climate model in order to study the short and long term impacts on the Atlantic Meridional Overturning Circulation.

Vidi project: From ice to deep ocean, where does the freshwater go.

In summer 2018 I was awarded a NWO Vidi grant, which I will use to study the effect of the freshwater fluxes from Greenland’s ice cap on deep water formation.

The Greenland ice cap is shrinking due to melting and calving of it’s marine terminating glaciers. Modelling studies have shown that this freshwater flux has the potential to significantly affect the North Atlantic circulation. Estimates of the Greenland freshwater flux have improved much over recent years, however it is still not know where and how much freshwater leaves the Greenland boundary current system (which holds freshwater from the Arctic Ocean as well as meltwater from Greenland) and enters the open ocean.

In this project we will deploy surface drifters in the East Greenland Current in the summers of 2019 and 2020. These drifters will show where exchange between the boundary current and the Atlantic Ocean takes place, how much mixing (dilution) of the freshwater occurs and whether the deep water formation regions are affected.

NACLIM/OSNAP Irminger Current array

As part of an international collaboration between the US, UK, Germany, Netherlands, Canada and China the Netherlands Institute for Sea Research (NIOZ) deployed a moored array on the western flank of the Mid Atlantic Ridge. These 5 moorings (four tall and one short) will sample the northward flow of warm, saline water in the Irminger Current in the upper water column as well as the dense North East Atlantic Deep Water (also called Iceland Scotland Overflow Water) in the lower water column.

National Initiative Changing Oceans (NICO)

Leg 4: Eddies of the Caribbean

In February 2018 I was expedition leader of NICO leg 4 on RV Pelagia. During this leg, from Aruba to Sint Maarten, we investigated an anti-cyclonic eddy in the Caribbean Sea. This project is together with TUDelft, where these eddies are being modelled, and Wageningen Marine Research, where they are interested in the impact of eddies on local fauna.

Pathways to Denmark Strait

The cold water that overflows the shallow sill of Denmark Strait (aptly named Denmark Strait Overflow Water or DSOW) is the densest constituent of North Atlantic Deep Water, which forms the deep southward return flow in the Meridional Overturning Circulation. There are multiple possible sources of DSOW.

It (or part of it) may flow south from the Greenland Sea in the East Greenland Current, or (part of) it may be formed more locally in the Iceland Sea and flow west in the North Icelandic Jet.

To illumanite the pathways of dense water to the Denmark sill RAFOS floats were deployed in the Iceland Sea. The first batch of 26 floats was deployed in July 2013, the second batch of 26 floats was deployed in July 2014. These floats can be tracked using the signals of six sound sources moored in the Iceland Sea.

Funded by NSG grant# 1259210: de Jong & Bower, in collaboration with Henrik Soiland of the Institute of Marine Research, Bergen, Norway.

Meso-scale eddies in the Labrador Sea

The Labrador Sea is one of few regions where deep convection occurs. During strong winters the surface waters are cooled to the point where they become dense enough to sink and mix with deeper waters. This process forms a cold water mass called Labrador Sea Water that extends from the surface down to 1 to 2 km deep. During spring and summer the central Labrador Sea restratifies. The warm, saline water responsible for the restratification is thought to originates from the Irminger Current along the west Greenland shelf. Due to a sudden steepening of the shelf the current becomes unstable and sheds warm-core eddies. These eddies can transport heat and salt to the interior basin.

Simulated eddies in the Labrador Sea

Even though measurements from the real ocean are great, they cannot capture everything we want to see. We simply cannot be everywhere at the same time (or if we tried it would be tremendously expensive). So therefore we use model simulations. For the eddies in the Labrador Sea we looked at the FLAME model (Family of Linked Atlantic Models Experiment). The FLAME model simulation is run at 1/12º or ~ 4 km. This resolution allows it to simulate the small eddies we’re looking for. The model run covers 15 years, between 1990 and 2005, which enables us to study different forcing conditions.

The model reasonably simulated the warm core anti-cyclones shed off the west coast of Greenland. Their size and core properties are very similar to the eddies we observed with the mooring. The model eddies do seem to stick to the topography more and closely follow the 3 km isobath. We determined that the coherent eddies provide about 20% of the heat transport from the boundary to the interior. A much larger part of the transport seems to be maintained by the non-coherent anomalies, which are smaller but greater in number.