| NSF Org: |
OCE Division Of Ocean Sciences |
| Recipient: |
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| Initial Amendment Date: | March 21, 2014 |
| Latest Amendment Date: | March 21, 2014 |
| Award Number: | 1357078 |
| Award Instrument: | Standard Grant |
| Program Manager: |
Baris Uz
bmuz@nsf.gov (703)292-4557 OCE Division Of Ocean Sciences GEO Directorate for Geosciences |
| Start Date: | April 1, 2014 |
| End Date: | March 31, 2018 (Estimated) |
| Total Intended Award Amount: | $223,089.00 |
| Total Awarded Amount to Date: | $223,089.00 |
| Funds Obligated to Date: |
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| History of Investigator: |
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| Recipient Sponsored Research Office: |
8622 DISCOVERY WAY # 116 LA JOLLA CA US 92093-1500 (858)534-1293 |
| Sponsor Congressional District: |
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| Primary Place of Performance: |
9500 Gilman Dr, MC 0224 La Jolla CA US 92093-0224 |
| Primary Place of
Performance Congressional District: |
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| Unique Entity Identifier (UEI): |
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| Parent UEI: |
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| NSF Program(s): | PHYSICAL OCEANOGRAPHY |
| Primary Program Source: |
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| Program Reference Code(s): | |
| Program Element Code(s): |
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| Award Agency Code: | 4900 |
| Fund Agency Code: | 4900 |
| Assistance Listing Number(s): | 47.050 |
ABSTRACT
Overview: The main reasons to identify the spatial and temporal distribution of mixing and upwelling in the deep ocean are to understand its energy budget, to close the overturning circulation and to understand deep currents and the transport of heat, fresh water, dissolved carbon, geochemical tracers, and nutrients. Observations suggest that the majority of deep-ocean mixing happens over rough topography, like the flanks of the world's mid-ocean ridges. Though tidally-driven internal waves are the most commonly discussed explanation for this mixing, a number of observations suggest that mixing and upwelling within the ridge flank canyons is significant, and that it is not fully explained by internal wave processes. There are about 1,000 mid-ocean ridge flank canyons in the deep ocean, and the canyon to be studied in this project is representative of many or most of them. Therefore, if boundary layer processes are shown to be significant in this canyon, they are expected to be significant throughout much of the world's oceans. This study presents a novel hypothesis for the mechanism behind an important process (abyssal mixing), developed with physical models, and which can be feasibly and cleanly tested with an observational program.
Intellectual Merit: A novel mechanism for abyssal mixing and upwelling is proposed: diffusion-driven boundary layers interacting with complicated topography. Though it occurs in conjunction with tidally-driven mixing, this mechanism may significantly change the expected distribution of deep-ocean mixing. This project investigates whether boundary layers are driving the circulation within a canyon in the South Atlantic using a series of modeling experiments to elucidate how these boundary layers interact with complicated topography and affect bulk properties of the ocean. The approach consists of a hierarchy of models with increasing complexity, from canyons with constant cross-sections to fully-realistic three-dimensional topography. A key deliverable is a set of metrics for the total impact of the boundary layers on the density field far from the boundary. These metrics will be related to the characteristics of the topography as a first step toward mixing parameterizations that do not collapse all topographic effects into a single roughness parameter.
Broader Impacts: This project will improve our understanding of mixing and upwelling throughout the deep ocean. A key goal of the modeling portion of this study is beginning to develop mixing parameterizations for global models that take into account boundary layer and mixing processes within canyons and are based on both models and observations. This project will also form a central portion of the training of a postdoctoral researcher.
PUBLICATIONS PRODUCED AS A RESULT OF THIS RESEARCH
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PROJECT OUTCOMES REPORT
Disclaimer
This Project Outcomes Report for the General Public is displayed verbatim as submitted by the Principal Investigator (PI) for this award. Any opinions, findings, and conclusions or recommendations expressed in this Report are those of the PI and do not necessarily reflect the views of the National Science Foundation; NSF has not approved or endorsed its content.
We used a numerical ocean model to investigate the effects on ocean mixing of a diffusive bottom boundary layer in an idealized ocean canyon (Dell & Pratt, 2015).
We carried out a set of simulations with an ocean general circulation model (GCM) and used them to show that surface forcing in the Southern Ocean influences the stratification of the global ocean over a wider depth range than previously believed (Sun et al., 2016), but that it has less influence on the depth of the global overturning circulation than had been suggested previously (Sun et al., 2018). This work has implications for ocean outgassing of CO2 during glacial-interglacial cycles, as well as changes in ocean carbon uptake during the coming century.
We used GCM simulations in concert with an idealized ocean circulation model to investigate the sensitivity of the Antarctic Circumpolar Current to the Atlantic meridional overturning circulation (Sun and Liu, 2017), and we used an idealized ocean circulation model to investigate the relationship between the circulation in the South China Sea and (i) the North Pacific double-gyre system (Yang et al., 2017a) and (ii) intraseasonal variations of the summer monsoon (Yang et al., 2017b).
We also carried out research investigating the role of icebergs in the ocean climate system. We developed a new Lagrangian model for iceberg transport and decay (Wagner, Dell, & Eisenman, 2017), developed a new representation of iceberg capsizing that corrects a number of subtle errors that existed in many previous iceberg models (Wagner et al., 2017), and showed how biases in simulated ocean and atmosphere circulations and temperatures influence the distribution of iceberg meltwater when an iceberg model is included in a GCM (Wagner and Eisenman, 2017). We also proposed a theory for how icebergs traveled so far in the Atlantic Ocean during the Heinrich Events of the last glacial period (Wagner et al., 2018).
We investigated sea ice in comprehensive GCMs, showing that simulated Arctic sea ice trends became more consistent with observations in the current generation of climate models compared with the previous generation due to the inclusion of volcanic forcing (Rosenblum and Eisenman, 2016), but that sea ice trends in current GCMs still only match observed Arctic sea ice retreat in simulations which have biases toward too much global warming during the same time period (Rosenblum and Eisenman, 2017). We investigated how biases in Arctic sea ice retreat such as these can influence GCM projections of the timeline for reaching the targeted levels of global warming laid out in the Paris Climate Accord (Pistone et al., submitted 2018). Lastly, the we reviewed trends and variability in Southern Ocean surface conditions in modern observations, proxy reconstructions, and climate model simulations (Jones et al., 2016).
Last Modified: 06/12/2018
Modified by: Ian Eisenman
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