Anna Cabre

Climate and Oceanography

I study the output of Earth System Models to understand the large scale spatial and temporal variability of oceanic and atmospheric climate patterns, once the everyday weather has been averaged out. I am interested in predicting the mid and long-term changes due to climate warming and to separate these changes from natural variability. See below the main lines of research I am involved with.

See publications

South Atlantic transfer

We study regions that contribute to the northward heat transfer that occurs in the top 1000m of the Atlantic Ocean. The South Atlantic plays a crucial role in the returning limb of the Atlantic meridional overturning circulation that originates with sinking of cold and salty sater in the North Atlantic; the South Atlantic is the only basin that transfers heat equatorward from the subtropics to the tropics to compensate (northward) for the southward export of North Atlantic Deep Water (NADW), but it has traditionally not studied as much as the homologous North Atlantic. We have used a lagrangian technique to track the origin and path of the waters that end up in the subtropical or tropical gyres. We study the volume transport associated to each route, the paths of propagation, the spatial and depth structure of these paths, and the heat and freshwater gain along these pathways. Here a copy of the published paper.

Open-ocean deep convection in the Southern Ocean

During the mid-1970s, a huge hole in the sea ice (polynya) opened during winter in the Weddell Sea, east of the Antarctic Peninsula, and was observed with satellites that had been launched few years before. The polynya closed and has only reemerged during the last 2 winters. It is open-ocean strong water column mixing that brings relatively warm water from the deep ocean to the surface and melts the ice. All the models that have this mixing events predict a stoppage of mixing with climate warming. We have explored the variability in Southern Ocean surface temperatures that result from pulses in open-ocean deep convection in the Weddell Sea (in the Southern Ocean), with a long 1000-year control experiment with pre-industrial conditions that exhibits strong convective events every ~70 years. We have found that fluctuations in Southern Ocean surface temperatures modify the energetic balance at the top of the atmosphere and the propagation of heat transport in both the atmosphere and the ocean. The atmospheric changes result for example in a weakening of the Southern Ocean westerlies, a warming of the atmosphere, and an increase in precipitation towards the southern tropics. The oceanic changes result in a strengthening of the formation of Antarctic bottom waters, and a weakening of the Meridional Overturning circulation during convective events. See this communication release. Here a copy of the published paper.

Oxygen Minimum Zones in the Pacific

We analyse simulations of the Pacific Ocean oxygen minimum zones (OMZs) from 11 Earth system model contributions to the Coupled Model Intercomparison Project Phase 5, focusing on the mean state and climate change projections. The eastern tropical regions are often low in oxygen due to sluggish ventilation and strong biological activity that consumes lots of oxygen. Oxygen is essential for most types of oceanic life, hence it is crucial to understand these regions and the predicted evolution within the next century. The simulations tend to overestimate the volume of the OMZs, especially in the tropics and Southern Hemisphere. Under the climate change scenario RCP8.5, all simulations yield small and discrepant changes in oxygen concentration at mid depths in the tropical Pacific by the end of the 21st century due to an almost perfect compensation between warming-related decrease in oxygen saturation and decrease in biological oxygen utilization. See publication (pdf)

Phytoplankton modeling

Understanding how global phytoplankton populations will respond to climate change is critical, since phytoplankton provide the ultimate food source for all marine organisms and draw down atmospheric CO2 by fixing inorganic carbon into organic matter via photosynthesis. We analyzed for the first time all 16 Coupled Model Intercomparison Project Phase 5 models with explicit marine ecological modules to identify the common mechanisms involved in projected phytoplankton biomass, productivity, and organic carbon export changes over the twenty-first century in the RCP8.5 scenario (years 2080–2099) compared to the historical scenario (years 1980–1999). All models predict decreases in primary and export production globally of up to 30 % of the historical value. ("Consistent global responses of marine ecosystems to future climate change across the IPCC AR5 earth system models")
We also analyzed how phytoplankton change in the Southern Ocean. The models predict a zonally banded pattern of phytoplankton abundance and production changes within four regions: the subtropical ( 30 to 40 S), transitional (40 to 50S), subpolar (50 to 65S) and Antarctic (south of 65S) bands. We find that shifts in bottom-up variables (nitrate, iron and light availability) drive changes in phytoplankton abundance and production on not only interannual, but also decadal and 100-year timescales – the timescales most relevant to climate change. ("A latitudinally banded phytoplankton response to 21st century climate change in the Southern Ocean across the CMIP5 model suite")
See this outreach article summarizing our research.

Phytoplankton observations from satellite color data

Recent technological evolution has allowed the observation of phytoplankton abundance from space. When the Earth is not covered in clouds, satellites can see through to the surface of the Earth, and transform the ocean color into phytoplankton abundance with algorithms that use Chlorophyll as an indicator of mini-algae presence. Chlorophyll is a green pigment found in plants, responsible for absorbing the light needed for the photosynthesis. Hence, greener parts of the ocean have more biological productivity.
However, Chl and phytoplankton abundance do not follow a linear relation, as Chlorophyll can photoadapt differently depending on the light, nutrients, and temperature. I have been working with Tihomir Kostadinov and the group at UPenn on a novel bio-optical algorithm that retrieves size-partitioned phytoplankton carbon from ocean color satellite data, independently from Chlorophyll. This alrogithm is based on backscattering; the size of phytoplankton changes the spectrum of the light when scattering. We have studied the seasonality, interannual variability (associated to well known indices such as 'El Niño'), and long-term trends for phytoplankton and the different sizes in comparison to Chl, and have detected interesting differences across biomes.
Carbon-based phytoplankton size classes retrieved via ocean color estimates of the particle size distribution
Phenology of Size-Partitioned Phytoplankton Carbon-Biomass from Ocean Color Remote Sensing and CMIP5 Models
Inter-comparison of phytoplankton functional type phenology metrics derived from ocean color algorithms and Earth System Models

Effect of climate change on fisheries

Climate change is going to affect the habitat conditions that ultimately affect fisheries. Changes in temperature, stratification of the water column, wind patterns, food supply, all these modify the biomes where fish live. I have collaborated with a group from the Marine Research Division at AZTI that use the output of models to predict how the habitat of tuna, eel, anochovy is going to change in the next 50-100 years. See the recently published paper on 'Historical trends and future distribution of anchovy spawning in the Bay of Biscay'

Publications

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