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

• Main Author: Koelling, Jannes
• Other Authors: Send, Uwe
• Format: Other/Unknown Material
• Language: English
• Published: eScholarship, University of California 2020
• Subjects: Physical oceanography; Chemical oceanography; Climate; Ocean circulation; Oceanography; Labrador Sea; Nordic Seas; North Atlantic Deep Water; North Atlantic
• Online Access: https://escholarship.org/uc/item/30h7h4bk

North Atlantic Deep Water is found in much of the deep Atlantic Ocean, and its formationin the Labrador and Nordic Seas and subsequent southward export are a vital part of globalocean circulation and Earth’s climate system. The overarching goal of this dissertation is tobetter 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 oxygenassociated with deep convection in 2014–15. The results show that intense air-sea exchangeresults in an uptake of 29.1 ± 3.8 mol m^−2 during the convective season, with much of the fluxbeing 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 thesummertime productive season. Lateral fluxes are found to play an important role for the carbonand nitrate budgets immediately below the mixed layer, with respiration rates underestimated byup to 50% if they are ignored.In chapter 3, gravity measurements from satellites are used to investigate variability in oceancirculation. After trends in the data are validated using independent measurements, they are usedto 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 southwardflow in the Deep Western Boundary Current.A twenty-year record of mooring data is analyzed in chapter 4 to investigate changes in NorthAtlantic Deep Water transport at 16 ◦ N. Multi-decadal variability is observed in the transport timeseries, and is largely associated with density changes in the lower half of the North Atlantic DeepWater layer, which in turn appear to be caused by changes in the source region. The data are alsocompared to another transport time series at 26 ◦ N, and similarities and differences are discussed.