Seasonal Mixing of the Irminger Sea Water Column

Seasonal deep mixing in the North Atlantic is a key process in the Atlantic Meridional Overturning Circulation (AMOC), as surface waters are mixed into the deep ocean carrying with them heat, nutrients, dissolved gases, and organic matter. This circulation is a key component of the earth’s climate system and the global carbon cycle. These data highlight the seasonal mixing cycle around the OOI Global Irminger Sea Array, a location of deep water formation, as exhibited through its temperature and salinity at three depths within the water column (surface, mid, and deep waters).

During the winter months, surface waters cool as heat radiates from the warm southern waters that flow into the Irminger Sea into the atmosphere. Additionally, strong winds and storms mix the water column leading to be similar temperature and salinity throughout the water column in winter months. During the summer months, the winds calm and the water column stratifies. This stratification is caused by two processes, first, the surface layers are warmed by the sun leading to temperatures close to 10oC while bottom layers remain cold; second, surface salinity decrease as winter ice melts.

By capturing these annual cycles across decades, scientists can observe variation between years, discover drivers of that variation, and distill long term trends in annual mixing patterns.

 Seawater temperature and salinity data from three CTDs (30, 180, and 1500m depths) on the Global Irminger Flanking Mooring B from Sept 2014 – Aug 2017 (Deployments 1-3).

Access the Data

Disclaimer: data used in this example and provided in the .csv file were downloaded from the OOI on Oct 18, 2019. The file format and/or contents could have changed if downloaded directly from OOI Net after this date.

Access from OOI Net:
GI03FLMB-RIM01-02-CTDMOG060 (30m)
GI03FLMB-RIM01-02-CTDMOG065 (180m)
GI03FLMB-RIM01-02-CTDMOH071 (1,500m)

Pull Data Using Python Code. Code demonstrates how to download CTD data from multiple instruments on the Flanking Mooring using the Machine-to-Machine (M2M) interface, remove outliers, calculate hourly averages, and export the data as a .csv file.

Data Review Pages:
30m CTD
180m CTD
1,500m CTD

Global Irminger Flanking Mooring B (GI03FLMB)

Location: SW of Greenland in the Irminger Sea
Lat/Lon: 59.7155°N, 39.3148°W
Water Column Depth: 2,800m
Platform: Mooring Riser
Instruments: CTD (CTDMO-G & CTDMO-H) – fixed on inductive wire

Graphics Credit: OOI Cabled Array program & the Center for Environmental Visualization, University of Washington

Essentials of Oceanography Textbook Sections

5.2 What important physical properties does water possess?
5.6 How does seawater salinity vary at the surface and with depth?
5.7 How does seawater density vary with depth?
7.3 What causes upwelling and downwelling?
7.5 How do deep-ocean currents form?
16.4 What changes are occurring in the oceans as a result of global warming?
16.5 What should be done to reduce greenhouse gases?

For more details, check out the full “Textbook Crosswalk”

Next Gen Science Standard Connections

HS-PS3-4. Plan and conduct an investigation to provide evidence that the transfer of thermal energy when two components of different temperature are combined within a closed system results in a more uniform energy distribution among the components in the system (second law of thermodynamics). This dataset illustrates a stratified water column where each layer has a different temperature, then as the water column mixes those water temperatures change to become uniform.

Additional Resources

Data Exploration – Thermohaline Circulation
Overturning in the Subpolar North Atlantic Program
The North Atlantic Aerosols and Marine Ecosystems Study (NAAMES) – Science Objectives

OOI Science Theme

Climate Variability and Ecosystems

Related Publications

de Jong, M.F., et al. 2018. Deep convection in the Irminger Sea observed with a dense mooring array. Oceanography 31(1):50–59.

Palevsky, H.I., and D.P. Nicholson. 2018. The North Atlantic biological pump: Insights from the Ocean Observatories Initiative Irminger Sea Array. Oceanography 31(1):42–49.

de Jong, M. F., and L. de Steur. 2016. Strong winter cooling over the Irminger Sea in winter 2014–2015, exceptional deep convection, and the emergence of anomalously low SST. Geophysical Research Letters 43:7106–7113.