When we study navigation and seamanship in the Navy School, we go back to the traditions of the old navigators; those that more than two millennia ago followed their instincts and understanding of the signs drawn from the natural world: winds, clouds, oceanic currents, stars and tides. Nature somehow taught us it’s jargon and we learnt how to sail across the seas following her signs. Scientific breakthrough and technological innovation did the rest to accomplish all the magnificent explorations and discoveries we have accomplished, but despite how much we have progressed, even today, we still follow the cues of nature when we sail across the ocean.

         At the beginning we were constrained and feeling comfortable in the Mediterranean. When European navigators entered the Atlantic Ocean in the fifteenth and sixteenth centuries  we quickly became aware of how lost we were. The Jacob’s staff and Quadrant helped us locate ourselves by latitude, and the lateen rigging provided the benefit to sail windward in small crafts like caravels. Even after Columbus made it across into the Caribbean in 1492, we used to get lost in the Atlantic and come back to Europe by the benevolence of mighty currents and forgiving wind systems that circle the Atlantic in a clockwise direction. Each time we came back we built more knowledge and understanding of the Atlantic’s Ocean-Atmosphere interactions systems known today as the North Atlantic Gyre. 

         Amongst the currents the North Atlantic Gyre is composed of the most influential one is the Gulf Stream. The Gulf Stream originates in the warm waters of the Gulf of Mexico where it swiftly exits through the Straits of Florida following the eastern coastline of North America into the Grand Banks of Newfoundland. There it bends to the East extending into the North Atlantic Drift where it splits in two branches, a northern and colder direction into the North Sea and a warmer and southeasterly direction into the Canary Islands. In the Atlantic Basin the Gulf Stream and the North Atlantic Drift regulate the climate from Florida to Newfoundland and the coasts of North and Western Europe. During millennia, these currents have shaped the climate and therefore life and history in the European and North American continents.  

         But not all happens on the surface. These currents are the limbs of a much broader system of ocean-spanning currents known as the Atlantic Meridional Overturning Circulation (AMOC): a system of surface and deep currents influenced by wind stress and thermohaline circulation that distributes heat across the planet. This complex network of currents powered by heat, salinity and wind, transport vast amounts of energy and nutrients from the tropics into the North Atlantic like a conveyor belt. The warm and saline water of the Gulf Stream loses temperature and cools down in the North Atlantic where it sinks into the deeper layers of the abyssal ocean traveling South on a thousand year voyage across the oceans.       

         The influence of AMOC is considered unique in the world’s oceans and is believed to be responsible for the warmer milder climate of the northern hemisphere, specially northwestern Europe. AMOC also represents a very important carbon sink in the northern hemisphere sequestering around 0.7 billion tons of Carbon yearly (0.7PgC/year).

         Before the grandiose power of the Atlantic’s Ocean-Atmosphere system, we face an existential climate crisis where we look like ancient mariners living at the whims and mercy of currents and winds. The stability of the AMOC seems to be extremely relevant to our livelihood and climatic stability. Changes in the AMOC and its enormous tentacles of water will impact atmospheric circulation and consequently will influence rainfall, temperatures, winds, sea levels and hurricane patterns from the Sahel to Greenland and Mesopotamia to Minnesota. This potential change is one of the “tipping points” that scientists have their eyes on.

         Like a game of “jenga”, tipping points represent changes in climate that can push the earth’s systems that sustain life into abrupt and irreversible conditions. A breakdown of the Atlantic Circulation by the slowing down of the AMOC would cause a disruption of the oceanic ecosystem. 

         The AMOC is highly dependent on salinity and temperature gradients in the ocean and scientists suspect that the AMOC is slowing down in response to anthropogenic global warming. Paradoxically, everywhere in the planet temperatures are rising due to the greenhouse gases emissions into the atmosphere, but a region in the subpolar North Atlantic close to the Southern tip of Greenland is cooling down because of the melting of its ice sheets. This cold blob is called by scientists the North Atlantic warming hole

Scientists argue that sudden introduction of freshwater into the North Atlantic could be disturbing the sinking of denser saltier water coming from the tropics in the Gulf Stream, overturning the critical phase of the AMOC that drives the circulation when warm water cools and sinks reversing its direction deep into the Atlantic Ocean. This regional reduction in the surface ocean density, driven by changes in accumulated freshwater input from the Greenland Ice Sheets has become critical to understand what is happening in the AMOC and its relation with a weakening Gulf Stream current. This freshwater event was described in an article published in 1988 by Dickson, R. et al called “The Great Salinity Anomaly” as “one of the most persistent and extreme variations in global ocean climate yet observed in this century”.

  We have no certainty of the impact a shutdown of the AMOC will have on the climate. Scientists have dung in the past thousands of years and more recent behavior of AMOC and the news are troubling. Slowing down or even shutting down of the currents in the Atlantic could accelerate sea level rise, strengthen hurricanes, exacerbate global heating, bring extreme warming into Europe to the scale of the Sahara desert, change the planet’s radiation budget, disturb the general circulation of gases in the atmosphere and modify the ability of the ocean to absorb one third of human carbon dioxide emissions.

Like the Flying Dutchman, we live today wandering around a sea of uncertainty. As an everyday person, I do not know how I can contribute to avoid this. Despite all the progress we have accomplished we are again sailing at the whims of  mighty currents and forgiving wind systems that circle the Atlantic.