Note: Now that I'm back home, I still have a lot to share! I'll be writing new journals about the science of MOSAiC every week or so, and updating photos on prior journals with ones taken during my PolarTREC Expedition. This week, revisit my September Equinox journal for updated photos.
After traveling through approximately nearly 20 time zones (I honestly lost count!), I am comfortably at my husband's house in Washington state. With help from PolarTREC, I was able to arrange my flights so that I could extend my layover on the way through Iceland. Soaking in hot springs and hiking through mossy mountain valleys was the perfect counterbalance for 6 weeks on an icebreaker and in the sea ice. Then, I visited friends in New York City and family in northeastern Pennsylvania. Breaking up the journey like this was fun, but also a practical way to avoid total burnout from jet lag and to combine multiple purposes so that I was able to cover more of my own travel needs and desires with the same carbon emissions.
I am back to work for the Center for Alaskan Coastal Studies, and currently busy with two different funding proposals as well as planning for student groups that will visit our remote (though not as remote as MOSAiC!) Field Station in 2020. When I can, I also help out with farm chores here at Nathan's. My favorite task is helping to socialize the piglets born just a few weeks before I left on MOSAiC. This mostly involves sitting with them and giving them treats!
In my spare time, my favorite farm chore is helping to socialize the piglets by sitting with them and feeding them treats. Photo credit: Nathan Main, 2019.
Having come such a long distance from MOSAiC, it is easy to feel like I am in a totally different world than the Arctic. But the connections between the Arctic and this part of the world -- really all parts of the world -- are strong and a part of what the MOSAiC Expedition is seeking to better understand. One way that these connections manifest are in the global movements of water through the oceans. Which brings up a question that many readers asked, and that I see frequently in media.
"Will climate change break the ocean conveyor belt?"
Global patterns of large-scale ocean currents, sometimes referred to as the ocean conveyor belt, play a huge role in all sorts of processes around the planet. For example, by bringing warm surface water north in the Atlantic Ocean, these ocean currents make northern Europe a much warmer place than it would be otherwise. The sinking of water from the ocean's surface during the winter in the northern Atlantic completes the conveyor belt current that runs towards the equator at the ocean bottom. Importantly, carbon dioxide and heat in the atmosphere are absorbed near the ocean surface and then trapped as these surface waters sink. In this way, heat and carbon dioxide are moved from the atmosphere into the huge mass of the ocean. This process acts as a buffer to dampen the effects of climate change.
This image, from the National Oceanic and Atmospheric Administration, depicts the major flows of global ocean currents. Blue denotes cold water, and red denotes warmer water.
It is clear that the ocean conveyor belt is important. What isn't clear at all is how large-scale ocean currents will be affected by climate change.
One thing that researchers are concerned about is what will happen with freshwater in a changing Arctic. In some ways, the Arctic Ocean is really a big estuary -- a place where saltwater and freshwater mix together. Currently, many rivers spill freshwater into the Arctic Ocean. Climate change may affect how much precipitation flows from the land into these rivers and then into the sea; it may also affect the timing of this input of freshwater. Patterns of precipitation and evaporation over the ocean may change too.
Also, some warmer water from the Pacific Ocean enters the Western Arctic Ocean from the Bering Strait; how much and when these pulses of heat are added will affect ice formation and retreat. This is still poorly understood, but we do know that adding heat in the Arctic system increases ice melting. Sea ice has a low salinity, so melting sea ice adds surface freshwater to the Arctic system.
The Arctic already stores and releases freshwater in pretty unpredictable ways. But in a changing Arctic, the ocean may have the capacity to store more freshwater and then also release more freshwater. One important question is where this freshwater will end up. This depends on how much freshwater there is and where it enters the Arctic. It also depends on how atmospheric processes drive winds, and how these winds move ice and water. As the central Arctic ice pack melts more, and river flows increase, it is likely that this extra fresh surface water and ice flow out across the Central Arctic Ocean into the North Atlantic. And here it would overlap with the Atlantic surface water involved in deepwater formation and global ocean circulation.
Much of the freshwater from Arctic lands, like this small forest stream, eventually flows into the Arctic Ocean, where it can impact currents.
So why does the Atlantic surface water sink? How would increased freshness of the surface water impact this?
In the Atlantic Ocean, one major surface current is called the Gulf Stream. The Gulf Stream carries water northeast from the East Coast of North America to the North Atlantic near England. As this water moves through hot air temperatures, some water evaporates and the surface water becomes saltier. Saltier water is denser than freshwater. Salty water will sink in freshwater. But cold water is also more dense than warm water. So this salty surface current stays above the cooler, slightly less salty Atlantic water for a while. However, as it reaches the North Atlantic in the winter, the salty water of the Gulf Stream begins to cool. Now there is cold, salty water. It begins to sink, and as it sinks it causes the water below to flow south along the ocean bottom. This is a big part of what keeps global ocean currents circulating.
North Atlantic deepwater formation doesn't happen everywhere in the North Atlantic Ocean. Conditions are best in the Greenland, Iceland, and Norwegian Seas and near Labrador. These are the places where salty North Atlantic water cools enough and is able to sink deep enough to push the global circulation along.
So could fresher surface water flowing into these areas interrupt the deepwater formation?
First of all, it is important to note that scientists are still unsure if climate change will cause more freshwater to be released into these areas. They don't know for sure that there will be more freshwater released by the Arctic in the future. And if there is more freshwater released, there are many questions about where exactly that water will end up. This is hard to observe in the field, but most numerical models show that the surface water has a lower salinity than it used to at some times of the year.
If it does happen that there is more freshwater flowing into these areas that are key for deepwater formation, there are at least two possible ways it could affect the process. If the freshwater mixes with the salty North Atlantic water before it has time to cool, this mixing process could create less salty water. With lower salinity, this water won't be as dense when it cools and won't sink as rapidly or as deep.
If the freshwater doesn't mix with the saltwater, it might form a thin layer on top of the salty North Atlantic water. This freshwater lens could form an insulating layer. Acting like a blanket, it could limit how heat moves between the saltwater and the air; because of this, the salty North Atlantic water might not cool as much. If it doesn't cool, it might not sink as rapidly or as deep. In both of these instances, it is possible that changes to how fast or how deep the water sinks could significantly slow down or disrupt global circulation patterns.
There is also a possibility that changes in the Arctic might shift where this deepwater forms. As ice extent decreases, warm Atlantic water might push farther towards the ice edge. Then deepwater formation might take place in the Arctic Ocean instead of the North Atlantic. What this would do to global ocean circulation is a big question.
Clearly, this is a complicated issue. Natural variability in the Atlantic Ocean makes it difficult to know for sure if and how deepwater formation has changed at all in recent decades. Much more research and modeling is needed to better understand all of this.
The interplay between the atmosphere and ocean creates both local and large-scale ocean currents. I took this photo as we left the sea ice behind and entered the more temperate Barents Sea.
Also complicated is teasing out the role of Arctic Ocean currents in the variability of Arctic systems -- and the way that climate change may be affecting these ocean currents. There are two major questions that many oceanographers are concerned about as the climate changes.
Currently, heat coming in with salty water from the Pacific and Atlantic Ocean is trapped well below the ocean surface. The Atlantic water, for example, has a specific density. As it flows into the Arctic Basin, it sinks or rises until it finds Central Arctic Ocean Water of a similar density. And then it spreads out at that level. This is called an intrusion of Atlantic water. Atlantic water tends to be found in the Arctic Basin at depths around 500m, compared with Pacific water at 200m. Because these waters are fairly deep, they can’t easily transfer their heat into the surface waters where it could affect sea ice, the atmosphere, and the upper ocean ecosystem.
However, researchers are not quite sure what will happen in the future. There is concern that more of the heat from this Pacific and Atlantic water might make its way to the surface waters of the Arctic Ocean through a variety of processes. This might be more likely to happen off the coast of Alaska because the Bering and Chukchi Seas are so shallow and the warm water is closer to the surface. In fact, there is some evidence that this may already be causing declines of seasonal sea ice near Alaska's coastline.
Scientists are also paying attention to how thinning sea ice might change the interactions between the atmosphere and the ocean. Thinner ice moves more easily, so wind stress is more easily transferred into movement of ocean water. Thinner ice, especially ice that is young and has less snow on it, is more transparent. When ice is more transparent, more energy from the sun is able to get into the water during the summer. Similarly, when the ice is more fragmented or more leads form, more energy from the sun is able to get into the water. This can change the amount of heat in the upper ocean available for ice melting. It can also affect how much and what type of phytoplankton is able to grow, with potential impacts to Arctic ecosystems.
In an Arctic with less sea ice, more energy from the sun will reach the ocean.
Changes to the ocean and sea ice can also in turn affect the atmosphere. If these patterns change, it could affect major wind patterns in the Arctic. This might then impact larger wind patterns like the Jet Stream. In fact, some scientists suggest this is already happening. The Jet Stream has a big influence on northern hemisphere weather, including the intensity and frequency of storms, so it is really important to understand these changes.
The atmosphere, ocean, sea ice, and biology in the Arctic are connected in many, many ways. This is a highly coupled system, which means all of these pieces affect and are affected by each other in a variety of ways. This makes it very hard to predict what will happen in a changing Arctic. It also makes scientific projects like MOSAiC very important. These expeditions allow scientists to study not just individual aspects of the Arctic but really focus on understanding the links between all of these different pieces.
Word of the Day The day I began this journal about Ocean Currents (October 23, 2019) we said goodbye to the helicopter crew and MI-8 helicopters. We came close to the Archangelsk coast and they flew to land. Their work with the Distributed Network is done and they have other projects to begin.
One of two MI-8 helicopters we used extensively in the set up of the distributed network for MOSAiC.
Some of us volunteered to help move the second helicopter out of the hangar. This required a lesson in basic Russian commands and directions. Vperyod directs you forward, and nazad is backward. Interestingly, verkh refers to the top of a surface while vverkh with two v-sounds means up. Stoy means stop or halt. When a group is pushing a huge helicopter around on the 5th floor deck of a ship in mildly rolling seas, knowing when to stop is important! Luckily, all went smoothly and the helicopters departed successfully. Now we will transit along the coastline back to Tromso.
Education Extension NOAA's Arctic Ocean Exploration: Current Events lesson for high school students utilizes Arctic Ocean data and two hands on activities to explore the driving forces of currents.
At the elementary or middle school level, the Center for Alakan Coastal Studies' Density Differences: Water Lesson introduces students to how temperature and salinity affect water density and drive ocean currents. It includes both lab activities and demonstrations by the teacher. But currents don't move in a straight line from high to low density areas. They are affected by coriolis and Eckman transport. Learn more about coriolis through Coriolis & Currents lesson which introduces students to the coriolis effect and how it influences currents in the ocean.
For elementary students, One World Ocean offers another hands on activity to learn about ocean currents and density differences between fresh and saltwater.
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