The global mean sea level rise caused by ocean warming and glacier melting over landforms such as Greenland is one of the most alarming aspects of a shifting global climate. However, the dynamics of the ocean and atmosphere further influence sea level changes region by region and over time. For example, along the U.S. East Coast, a pronounced acceleration of sea level rise in 2010-2015 was observed south of Cape Hatteras, while a deceleration occurred up North. These patterns provide background conditions, on top of which shorter-period (and often stronger) weather-driven sea level fluctuations compound what coastal communities directly experience day by day. Therefore, to develop or improve regional sea level predictions, it’s important to identify these patterns and explore how they change over time.
New Study Shows Atlantic Meridional Overturning Circulation and Mediterranean Sea Level are Connected
Ocean tracers such as heat, salt and carbon are perpetually carried by the global meridional overturning circulation (GMOC) and redistributed between hemispheres and across ocean basins from their source regions. The GMOC is therefore a crucial component of the global heat, salt and carbon balances.
Climate projections for the twenty-first century suggest an increase in the occurrence of heat waves. However, the time at which externally forced signals of anthropogenic climate change (ACC) emerge against background natural variability (time of emergence (ToE)) has been challenging to quantify, which makes future heat-wave projections uncertain. In a new article published in Nature Climate Change (Lopez et al., 2018), Hosmay Lopez and his team combine observations and model simulations under present and future forcing to assess how internal variability and ACC modulate US heat waves.
AOML oceanographers Christopher Meinen and Molly Baringer participated in the development of a new thirteen-year-long record of the daily Atlantic ocean overturning that has recently been released. This project is a collaboration between a large team of researchers at NOAA, at the University of Miami ,and at the National Oceanography Centre in Southampton, United Kingdom.
There have been many efforts to understand the role of the Atlantic Meridional Overturning Circulation (AMOC) as a potential predictor of decadal climate variability, motivated partly by its inherent relationship with North Atlantic sea surface temperature. In contrast, there is currently limited knowledge about the underlying mechanisms that govern the South Atlantic Meridional Overturning Circulation (SAMOC) variability and how it might feedback into climate, partly due to the small number of direct observations in this ocean basin.
Recent studies have suggested the possibility of the southern origin of the Atlantic MHT anomalies. These studies have used General Circulation Models (GCMs) to demonstrate covariability between the South Atlantic MOC (SAMOC) and the Southern Hemisphere westerlies at interannual to longer time scales. However, it has been pointed out that the sensitivity of the SAMOC to the changes in the Southern Hemisphere westerlies depends critically on the representation of mesoscale eddies in those models.
“Much of the work on the cause of Antarctic sea ice over recent decades has focused on atmospheric drivers but this paper focuses on the ocean’s role. The authors analyse the trend of Antarctic sea ice over the past 35 years on the basis of satellite data and model simulations forced with atmospheric reanalysis products. Their findings suggest that ocean processes play a crucial role in determining the seasonality of sea ice trends. They also reveal that the sea-ice response is regional.”
The Atlantic Meridional Overturning Circulation (AMOC) transports the upper warm water northward and the deep cold water southward in the Atlantic, and is a key component of the global energy balance. In many of the climate models that participate the Coupled Model Inter-comparison Project Phase 5 (CMIP5), the amplitudes of the AMOC agree very well with or are even larger than the observed value of about 18 Sv at 26.5N; but they still show cold upper ocean temperature biases in the North Atlantic.
The Meridional Overturning Circulation (MOC) plays a critical role in global and regional heat and freshwater budgets. Recent studies have suggested the possibility of a southern origin of the anomalous MOC and meridional heat transport (MHT) in the Atlantic, through changes in the transport of warm/salty waters from the Indian Ocean into the South Atlantic basin. This possibility clearly manifests the importance of understanding the South Atlantic MOC (SAMOC). Observations in the South Atlantic have been historically sparse both in space and time compared to the North Atlantic. To enhance our understanding of the MOC and MHT variability in the South Atlantic, a new methodology is recently published to estimate the MOC/MHT by combining sea surface height measurements from satellite altimetry and in situ measurements (Dong et al., 2015).
If you want to understand Earth’s climate and how it changes from year-to-year and decade-to-decade, look to the oceans, and follow the heat. The major driver in the redistribution of heat around the globe in the ocean-climate system is Meridional Overturning Circulation, or MOC. The MOC is a vertical circulation pattern that exchanges surface and deep waters via poleward movement of surface waters. As an example, the well known Gulf Stream on the eastern seaboard of North America carries warm water northward to the Greenland and Norwegian Seas, where it cools and sinks.