An Investigation of Abyssal to Mid-depth Variations in AMOC Properties and Transports through Observations and Assimilating Models

Statement of the Problem: To understand the causes of decadal-scale variability in Atlantic overturning waters it is necessary to both recognize and connect the changes that are occurring in a moving ocean. That is, from a climate perspective, there is a need to use available information to better understand not only how ocean properties are changing, but also how dynamics may be affecting changes. While models and re-analyses look to provide a moving and even predictive three-dimensional picture, both correct and incorrect details are often lost in integration of  available outputand deep signals, in particular, may be missing from numerical integrations. On the other hand, observations capable of providing details on the characteristics of deep ocean properties and processes are, more often than not, disconnected from one another in time.

Speaking to the AMOC competition’s aim to refine present knowledge of the AMOC state,  variability and change as well as NOAA’s long term goal of an improved understanding of the  changing climate system, the goals of this project are twofold: 1) to improve understanding of  changes in the deep South Atlantic Meridional Overturning Circulation (SAMOC) properties and transports through a statistical analysis and comparison of observations and numerical model  output, and 2) to develop an understanding of where and how two particular models are  succeeding and/or failing to capture observed deep signals thought to be signatures of climate  change. Repeat hydrographic lines will be used in combination with float data and Lowered Acoustic Doppler Current Profiles together with output from two high-resolution assimilative models (HYCOM and ECCO) to develop an understanding of what changes are occurring in the observed fields, where they are occurring, how such changes are or are not reflected in the numerical fields, and whether this matters. That is, what are the overall consequences to numerical prediction of discrepancies between modeled and observed deep and bottom water changes and transport? The observation-model comparative analysis is relevant to the AMOC competition’s aim of combining existing observations with models to refine our understanding of present-day and past AMOC circulation and transport. It is also relevant to NOAA’s goal of  informing future climate-scale predictions as it lo oks to determine the importance of specific  deep/abyssal pathways and particular regions of mixing to decadal simulations.

The proposed work includes a formal collaboration with Elaine McDonagh and colleagues at the  National Oceanography Centre in Southampton and informal collaborations with Edmo Campos  and SAMOC group working towards a long-term South Atlantic observational network, as well as Tonia Capuano at the Université de Bretagne Occidentale to assist in the calculation of mixing  estimates.