It turns out that volume does matter, particularly when it comes to the amount of cold dense water that forms off of the coast of Greenland and makes its way to the bottom of the sea floor. Surface water in the North Atlantic is cooled by arctic air and when ice sheets and icebergs form, the water left behind gets saltier and denser and sinks.
Density differences between the ocean’s surface and deep waters are what put into motion thermohaline circulation where the water that sinks pulls warmer less salty (less dense) water up from the equatorial regions to take its place. This global conveyor belt allows the ocean to take heat away from equatorial regions and distribute it throughout the planet.
Scientists know that deep water moves south in the Atlantic to Antarctica before it splits. One section of deepwater upwells in the Indian Ocean and the other in the North Pacific. This cold deep water that rises up to the surface brings with it vital nutrients to the base of the global food chain and to fisheries that feed millions of people in that region.
Ocean circulation not only transports heat, nutrients, marine life (think Finding Dory for a simple example) and carbon dioxide, but also influences climate patterns around the world. The Gulf Stream, which is a surface ocean current, is largely responsible for our climate here in the Southeast. Any changes to the global conveyor belt and the Earth’s ability to dissipate heat from the equator, geologically-speaking, has had a significant impact on global climate.
During the Last Glacial Maximum, which peaked around 21,000 years ago, ice sheets in North America went as far south as southern Illinois, pushing cool dry air south and changing both ocean and atmospheric circulation patterns to create a climate where mammoths, mastodons and other large Pleistocene mammals could call the Lowcountry home. At the end of the last ice age (around 10,000 years ago), ice sheets began to melt, initiating significant changes in climate which ultimately led to the extinction of those large mammals. They were replaced with the types of flora and fauna with which we are now familiar.
Changes over time
These types of large changes and feedback loops within our climate system have happened throughout geological time. But the reason we all need to pay attention now (and should have been since scientists have been shouting from the rooftops to wake up decades ago) is because humanity is at risk.
A recent study published in the journal Nature warns of a slow down and possible collapse of the oceanic conveyor belt soon — perhaps in just a few years. This study is supported by data from solid sources, including the Hadley Center at the University of Massachusetts Amherst (my alma mater for graduate school). While the study’s timing of the collapse will be debated, what is not debated is that there have been warning signs of a slowdown for decades that have largely been ignored. The Intergovernmental Panel on Climate Change’s last report stated a longer time period for a shutdown — by the end of the century. Regardless of the exact timing, changes have been happening and will continue to.
This year has been the hottest year on record globally and annual mean temperatures have been rising since 1880, having significant impacts on weather patterns and changing the climate. This has triggered a chain of impacts on rainfall, fisheries, farming and every possible sector of our human life. It is not debated by reputable scientists that warming is primarily caused by human activity, including the use of fossil fuels, changes in land use and our wasteful lifestyles. If you’ve been out of the loop, there’s no more excuse not to pay attention, educate yourself and get involved.
Toni Reale is the owner of Roadside Blooms, a unique flower, plant, crystal, rock and fossil shop in Park Circle in North Charleston. Formerly a geology instructor at the College of Charleston for over a decade, she remains passionate about environmental issues and interesting topics in science. roadsidebloomsshop.com
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