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Variability in formation, properties, and transport of North Atlantic Deep Water

  • Author(s): Koelling, Jannes
  • Advisor(s): Send, Uwe
  • et al.
Abstract

North Atlantic Deep Water is found in much of the deep Atlantic Ocean, and its formation

in the Labrador and Nordic Seas and subsequent southward export are a vital part of global

ocean circulation and Earth’s climate system. The overarching goal of this dissertation is to

better understand the processes controlling variability of North Atlantic Deep Water formation,

properties, and transport in the Atlantic Ocean.

Chapter 1 uses data from the central Labrador Sea during winter to estimate the uptake of oxygen

associated with deep convection in 2014–15. The results show that intense air-sea exchange

results in an uptake of 29.1 ± 3.8 mol m^−2 during the convective season, with much of the flux

being associated with injection of air bubbles. Chapter 2 looks at lateral fluxes of carbon, oxygen,

and nitrate from the Labrador Sea’s boundary current into the center of the basin during the

summertime productive season. Lateral fluxes are found to play an important role for the carbon

and nitrate budgets immediately below the mixed layer, with respiration rates underestimated by

up to 50% if they are ignored.

In chapter 3, gravity measurements from satellites are used to investigate variability in ocean

circulation. After trends in the data are validated using independent measurements, they are used

to study decadal circulation changes of North Atlantic Deep Water in the North Atlantic Ocean.

The analysis reveals a strengthening of the interior branch of North Atlantic Deep Water flow,

with transport increasing by 13.9 ± 3.7 Sv (1 Sv = 10^6 m^3 s^−1 ), balanced by a weaker southward

flow in the Deep Western Boundary Current.

A twenty-year record of mooring data is analyzed in chapter 4 to investigate changes in North

Atlantic Deep Water transport at 16 ◦ N. Multi-decadal variability is observed in the transport time

series, and is largely associated with density changes in the lower half of the North Atlantic Deep

Water layer, which in turn appear to be caused by changes in the source region. The data are also

compared to another transport time series at 26 ◦ N, and similarities and differences are discussed.

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