Greetings, everyone!
Hope you all (in America) are enjoying a nice Thanksgiving weekend. Out here in the Pacific Ocean, we're currently drilling what is most likely the second to last of the planned sites for the expedition. The seafloor at this site is about 3400 m (just over 2 miles) below the sea surface, so the cores are taking much longer to get brought up to the ship. It has been a nice respite from the rapid pace we had a couple weeks ago.
One of the good things about drilling in deeper water (beyond the slower pace of the cores) is that it is typically much easier to drill farther back in time. This is because the sedimentation rate at a given site generally correlates with the water depth of the site. Shallower sites tend to be closer to continents (which erode to provide a source of sediment) and have relatively high sedimentation rates. Deeper sites tend to be far away from continents and have very low sedimentation rates, as most of the sediment that erodes from the continents settles out of the water before reaching deeper water. So while the sediments 200 meters below the seafloor at some of the shallow sites we drilled earlier were less than half a million years old, they are much older (several million years old!) here.
While we don't get any days off during the expedition, we had a delicious Thanksgiving dinner a few days ago here complete with turkey, stuffing, and even some apple pie. The fruit and salad bars are slowly getting a little more barren (it has now been ~6 weeks since we left port and things are starting to go bad), but overall, the meals are still impressively good.
We had an aptly named "beginning of the end of the expedition" meeting earlier today. Our port call in Guam is now less than two weeks away. Looking forward to getting my land legs back!
Cheers,
Dan
Saturday, November 26, 2016
Saturday, November 19, 2016
Party Trick #565: Making an Ice Age Out of Pore Water
Greetings, friends!
We are presently in transit from our last couple sites to the west of Manus Island to our first of three planned sites along an area of the seafloor known as the Euaripik (rhymes with "terrific") Rise. This is a ridge along the seafloor that acts as a local high in topography; that is, it's sort of like an underwater mountain range. Still, its highest point is well over a mile beneath the sea surface!
Part of what I'll be doing at these next few sites is collecting pore water from the sediments to try to learn about how salty ocean was during the last ice age, or glacial period. How exactly does this work? First, think about all of the water that exists at Earth's surface: the water in the ocean's, underground, in rivers and lakes, and in the air around you. That's a lot of water, right? True, and it's also true that things like evaporation and precipitation can move this water around on Earth's surface. Most of water that falls out of the sky as precipitation actually evaporated from the ocean, but evaporation removes only the water from the ocean; the salts are left behind. This will become extremely important in a minute.
Twenty thousand years ago, parts of North America (including Canada, Wisconsin, and northern Illinois) and Europe were covered by a sheet of ice over a mile in thickness. Yeah, and you thought Midwest winters are brutal today! Anyways, the water in these ice sheets came from precipitation, most of which came from the ocean. But if a bunch of water that is in the ocean now was on land then, and the amount of water at Earth's surface was about the same, that means that there must have been less water in the ocean. And if there was less water in the ocean, that means the ocean must have been - you guessed it - saltier.
Now, we know from the above argument that the ocean as a whole must have been saltier at the end of the last ice age twenty thousand years ago; research by geologists suggests that sea level was actually over 300 feet lower then than it is today because so much water was taken out of the ocean and put on land as ice!* But exactly how much saltier is still unknown, and figuring out how much saltier different parts of the ocean were is really important for us to understand how the ocean and atmosphere may have transported heat differently during the Ice Age. This is in turn crucial for us to understand how and why ice ages start and end in the first place.
It turns out that looking at pore water from ocean sediments can help us tell how salty a given part of the ocean was during the last ice age. All water in ocean sediments ultimately starts as ocean water, meaning that if the ocean was saltier at a given time, the pore water in the shallowest sediments would also initially be saltier. This pore water and its salts get buried under more and more sediment over time. Although many of the salts in pore water participate in reactions in the sediment that change their concentration (or abundance), chloride (one of the ions that forms table salt, the most abundant salt in the ocean) does not. This means that as long as the pore water itself does not react with the sediment, pore water that starts off being saltier remains saltier as it is buried. And if we know how fast the sediment is being buried (that is, the sedimentation rate) and can measure the concentration of chloride (plus a few other things in order to make some minor corrections related to water temperature) - Presto! - we can tell how salty the ocean was during the last ice age!
Whew! Hopefully you've made it to this point and are still awake. Now you can impress your friends and win over your enemies with your impressive knowledge of the salty glacial ocean** at cocktail parties.
More cool party tricks next time!
- Dan
*This sea level drop was high enough to expose a strip of land that connected Alaska to Russia and would have allowed one to walk to Russia from Alaska and back....but shhh, let's not give Putin any ideas...
** "Salty Glacial Ocean" may or may not get confused for the name of a cocktail. Use with care.
We are presently in transit from our last couple sites to the west of Manus Island to our first of three planned sites along an area of the seafloor known as the Euaripik (rhymes with "terrific") Rise. This is a ridge along the seafloor that acts as a local high in topography; that is, it's sort of like an underwater mountain range. Still, its highest point is well over a mile beneath the sea surface!
Part of what I'll be doing at these next few sites is collecting pore water from the sediments to try to learn about how salty ocean was during the last ice age, or glacial period. How exactly does this work? First, think about all of the water that exists at Earth's surface: the water in the ocean's, underground, in rivers and lakes, and in the air around you. That's a lot of water, right? True, and it's also true that things like evaporation and precipitation can move this water around on Earth's surface. Most of water that falls out of the sky as precipitation actually evaporated from the ocean, but evaporation removes only the water from the ocean; the salts are left behind. This will become extremely important in a minute.
Twenty thousand years ago, parts of North America (including Canada, Wisconsin, and northern Illinois) and Europe were covered by a sheet of ice over a mile in thickness. Yeah, and you thought Midwest winters are brutal today! Anyways, the water in these ice sheets came from precipitation, most of which came from the ocean. But if a bunch of water that is in the ocean now was on land then, and the amount of water at Earth's surface was about the same, that means that there must have been less water in the ocean. And if there was less water in the ocean, that means the ocean must have been - you guessed it - saltier.
Now, we know from the above argument that the ocean as a whole must have been saltier at the end of the last ice age twenty thousand years ago; research by geologists suggests that sea level was actually over 300 feet lower then than it is today because so much water was taken out of the ocean and put on land as ice!* But exactly how much saltier is still unknown, and figuring out how much saltier different parts of the ocean were is really important for us to understand how the ocean and atmosphere may have transported heat differently during the Ice Age. This is in turn crucial for us to understand how and why ice ages start and end in the first place.
It turns out that looking at pore water from ocean sediments can help us tell how salty a given part of the ocean was during the last ice age. All water in ocean sediments ultimately starts as ocean water, meaning that if the ocean was saltier at a given time, the pore water in the shallowest sediments would also initially be saltier. This pore water and its salts get buried under more and more sediment over time. Although many of the salts in pore water participate in reactions in the sediment that change their concentration (or abundance), chloride (one of the ions that forms table salt, the most abundant salt in the ocean) does not. This means that as long as the pore water itself does not react with the sediment, pore water that starts off being saltier remains saltier as it is buried. And if we know how fast the sediment is being buried (that is, the sedimentation rate) and can measure the concentration of chloride (plus a few other things in order to make some minor corrections related to water temperature) - Presto! - we can tell how salty the ocean was during the last ice age!
Whew! Hopefully you've made it to this point and are still awake. Now you can impress your friends and win over your enemies with your impressive knowledge of the salty glacial ocean** at cocktail parties.
More cool party tricks next time!
- Dan
*This sea level drop was high enough to expose a strip of land that connected Alaska to Russia and would have allowed one to walk to Russia from Alaska and back....but shhh, let's not give Putin any ideas...
** "Salty Glacial Ocean" may or may not get confused for the name of a cocktail. Use with care.
Thursday, November 17, 2016
Stay Tuned!
Hi friends,
Life on the ship has been a bit crazy lately! We left the coast of Papua New Guinea a few days ago and are currently working on our fourth site in the past two weeks. For comparison, we completed two sites in the first four weeks of the expedition, so the pace at which we've been bringing up new sediments to look at and analyze has been quite quick.
We are presently some tens of miles to the west of Manus Island (an island north of Papua New Guinea) and will be heading further north within the next day or two to complete drilling at a couple more sites on our way toward Guam. It should be fun!
Gotta get back to work now, but I'll be back with the promised info on pore water and the last ice age soon. Also, hello to Mrs. Lennon's class! I had a wonderful time showing you around the ship last week and answering your great questions.
Cheers,
Dan
P.S. Check out my colleague Dr. Catherine Rose's geoscience education blog, On The Rocks, for a guest post with some photos later this week plus a smorgasbord of other interesting pieces that have already been posted: http://ontherocks.ie/.
Thursday, November 3, 2016
Don't Drink the Pore Water & Other Musings
Hi everyone,
We are still a couple days away from arriving at our next site off the northern coast of Papua New Guinea, which means more time for me to write. Woohoo! Things have been pretty nice for the past couple days. The paleontologists on the ship held an open house of sorts a couple evenings ago during which everyone else on the ship could come view some of the foraminfera and other tiny fossils that they have been looking at in the samples we've been bringing up to help determine the age of the sediments. It was great to have a chance to look at these fossils after having heard so much about them! Alas, my job on the expedition is not to look at fossils, but instead to squeeze water out of some sediment samples and analyze the chemistry of the water.
Wait a second, squeezing water out of sediments? Where does that water come from and why is it interesting? Imagine you are walking around on the seafloor and are able to pick up some sediment from the seafloor. It turns out that no matter what size of grains are in that sediment (e.g., sand or clay), the majority of what you would pick up would actually be just water - up to 70 or 80 percent water by volume! When sediment grains settle out on the seafloor, they do not do so in a very ordered manner, so there actually ends up being a lot of empty space between grains that gets occupied by water. This water is known as "pore water", as it occupies the "pore space" between grains in the sediment. The amount of pore space decreases as a given layer of sediment gets buried deeper and deeper by more sediments above, since the increased pressure added by the weight of the above sediments forces the grains to fit more closely together***. However, even sediments buried thousands of feet below the seafloor can be more than 20 or 30 percent water by volume, so there's always a bit of water that can be squeezed out.
To squeeze water out of sediment samples, we use a machine called a hydraulic press. When we place a sediment sample inside a squeezer assembly (basically, a metal cylinder with a hole at the bottom through which water can exit and a piston on top that presses down on the sediment), we use the force applied by this press to compact the sediments even more than they were beforehand and collect the pore water than exits as the amount of pore space decreases. The press can apply up to 30,000 ft lbs of force, or roughly 10,000 psi of pressure in our case. For comparison, the air pressure applied to keep a tire on your car inflated is typically ~30 psi. It's sort of like using a giant juicer where the sediment is your fruit and the water is your juice. Just don't drink the pore water, it's salty and not very nutritious for any living things larger than bacteria.
It probably seems a little silly to apply so much force and energy just to squeeze a bit of water out of some sediments. After all, there's a whole ocean of water above the sediments that we could sample without squeezing, right? However, the concentrations of various dissolved salts and nutrients within the sediments can tell us a lot about things that are going on within the sediments themselves. For example, there are a lot of microorganisms below the seafloor that live by eating the remains of dead organisms in the sediments and "breathing" with things like iron, nitrate, and sulfate instead of oxygen. Some of these chemical reactions in the sediments can affect the fossil material we're interested in using to tell us about climate change in Earth's past, so we gain a lot of important information on how much change the chemistry of the fossils has undergone by looking at the chemistry of the pore water.
Pore water can also tell us about the ice sheets that existed in North America and Europe around 20,000 years ago and why they may have disappeared. But more on that next time!
Staying afloat,
Dan
***You can actually demonstrate this the next time you go to the beach. If you step on wet sand, notice how a bit of water comes out of the sand as you put your weight on the sand to make a footprint. This water used to occupy empty space between the sand grains, and the compaction of the grains is what allows your footprint to remain intact once you step away!
We are still a couple days away from arriving at our next site off the northern coast of Papua New Guinea, which means more time for me to write. Woohoo! Things have been pretty nice for the past couple days. The paleontologists on the ship held an open house of sorts a couple evenings ago during which everyone else on the ship could come view some of the foraminfera and other tiny fossils that they have been looking at in the samples we've been bringing up to help determine the age of the sediments. It was great to have a chance to look at these fossils after having heard so much about them! Alas, my job on the expedition is not to look at fossils, but instead to squeeze water out of some sediment samples and analyze the chemistry of the water.
Wait a second, squeezing water out of sediments? Where does that water come from and why is it interesting? Imagine you are walking around on the seafloor and are able to pick up some sediment from the seafloor. It turns out that no matter what size of grains are in that sediment (e.g., sand or clay), the majority of what you would pick up would actually be just water - up to 70 or 80 percent water by volume! When sediment grains settle out on the seafloor, they do not do so in a very ordered manner, so there actually ends up being a lot of empty space between grains that gets occupied by water. This water is known as "pore water", as it occupies the "pore space" between grains in the sediment. The amount of pore space decreases as a given layer of sediment gets buried deeper and deeper by more sediments above, since the increased pressure added by the weight of the above sediments forces the grains to fit more closely together***. However, even sediments buried thousands of feet below the seafloor can be more than 20 or 30 percent water by volume, so there's always a bit of water that can be squeezed out.
To squeeze water out of sediment samples, we use a machine called a hydraulic press. When we place a sediment sample inside a squeezer assembly (basically, a metal cylinder with a hole at the bottom through which water can exit and a piston on top that presses down on the sediment), we use the force applied by this press to compact the sediments even more than they were beforehand and collect the pore water than exits as the amount of pore space decreases. The press can apply up to 30,000 ft lbs of force, or roughly 10,000 psi of pressure in our case. For comparison, the air pressure applied to keep a tire on your car inflated is typically ~30 psi. It's sort of like using a giant juicer where the sediment is your fruit and the water is your juice. Just don't drink the pore water, it's salty and not very nutritious for any living things larger than bacteria.
It probably seems a little silly to apply so much force and energy just to squeeze a bit of water out of some sediments. After all, there's a whole ocean of water above the sediments that we could sample without squeezing, right? However, the concentrations of various dissolved salts and nutrients within the sediments can tell us a lot about things that are going on within the sediments themselves. For example, there are a lot of microorganisms below the seafloor that live by eating the remains of dead organisms in the sediments and "breathing" with things like iron, nitrate, and sulfate instead of oxygen. Some of these chemical reactions in the sediments can affect the fossil material we're interested in using to tell us about climate change in Earth's past, so we gain a lot of important information on how much change the chemistry of the fossils has undergone by looking at the chemistry of the pore water.
Pore water can also tell us about the ice sheets that existed in North America and Europe around 20,000 years ago and why they may have disappeared. But more on that next time!
Staying afloat,
Dan
***You can actually demonstrate this the next time you go to the beach. If you step on wet sand, notice how a bit of water comes out of the sand as you put your weight on the sand to make a footprint. This water used to occupy empty space between the sand grains, and the compaction of the grains is what allows your footprint to remain intact once you step away!
Tuesday, November 1, 2016
Life on the Ship
Greetings, friends!
It has been a quiet few days on the ship, as we finished our second site a couple days ago and will be in transit for the next few days to our next site off the northern coast of Papua New Guinea. In contrast to where we've cored thus far off (off the coast of NW Australia), Papua New Guinea is chock full of incredibly active volcanoes. The sediments we bring up will likely contain a lot of ash and look different from what we've seen so far, so we're all looking forward to seeing something new.
Since things are pretty relaxed at the moment, I thought I'd take the time to tell you more about what life on a ship is actually like. After all, the first questions that come to mind for many folks are not about the science that we're doing, but about the more biologically necessary and day-to-day sorts of things: What do you eat? Do you have your own room on board? What are the bathrooms like? Etc. So, here we go.
The food on the ship is actually quite good. Since all of the scientists and drillers are divided into 12 hour shifts such that the boat can operate 24-hours a day, 4 meals per day are served on the ship. These happen at 5-7 am, 11am-1pm, 5-7pm and 11pm-1am, although most folks are theoretically asleep for at least one of the meals (the 5am-7am one for moi). We typically have our choice of three main dishes plus 4 or so veggies and side dishes at each meal, and a fruit bar and salad bar are also available. The fruit and salad bars will remain operational for another week or so (the kitchen has a special ozone refrigerator that keeps perishables fresh much longer than your typical one), but I'm told that eventually they disappear. To top it all off, there are always cookies, soft-serve ice cream, and other assorted desserts. Everything is basically all you can eat, so you can either think of it as heaven or an impending crime scene where your body fat % is the victim. I'm definitely eating a lot more here than I typically do at home (#gradstudentlife), so I've been having to exercise to compensate. But that's more of a compliment to the kitchen than a complaint, as it certainly could be much worse.
Almost every person on the ship shares a room with another person, as there are two bunks in each room. Every two rooms also shares a single shower and toilet, so you might imagine that things could get a little crowded. However, the organizers of each expedition make sure that your roommate works the opposite shift as you, so you are rarely or never in the room at the same time as your roommate and are generally only sharing a shower and toilet with one other person. I'm told that before the ship was renovated in 2008, there were actually four people to a room and still a single shared restroom for every two rooms. The ship apparently had some unsavory nicknames during that time, but things are cushy now in comparison.
The toilet system on the ship is a vacuum system much like that used on an airplane. Since carrying a two months worth of fresh water on board would be very heavy and a bit unfeasible, the boat is also equipped with a distillation and filtration system to make freshwater from seawater. The water tastes great, but it's so salt-depleted that many actually need to take vitamins or drink Gatorade once a day or so to compensate for the lack of electrolytes. Still, it's a bit funny to think that I'm drinking water so clean that I would normally have to pay for it back home.
Although the days are long and filled with collecting samples, running analyses in the lab, and writing, we still find time to step outside and enjoy some fantastic views of the sunset (or, every once in a while, of land) and stars from the ship's deck. Life is good!
Gotta get back to work, but until next time!
Cheers,
Dan
It has been a quiet few days on the ship, as we finished our second site a couple days ago and will be in transit for the next few days to our next site off the northern coast of Papua New Guinea. In contrast to where we've cored thus far off (off the coast of NW Australia), Papua New Guinea is chock full of incredibly active volcanoes. The sediments we bring up will likely contain a lot of ash and look different from what we've seen so far, so we're all looking forward to seeing something new.
Since things are pretty relaxed at the moment, I thought I'd take the time to tell you more about what life on a ship is actually like. After all, the first questions that come to mind for many folks are not about the science that we're doing, but about the more biologically necessary and day-to-day sorts of things: What do you eat? Do you have your own room on board? What are the bathrooms like? Etc. So, here we go.
The food on the ship is actually quite good. Since all of the scientists and drillers are divided into 12 hour shifts such that the boat can operate 24-hours a day, 4 meals per day are served on the ship. These happen at 5-7 am, 11am-1pm, 5-7pm and 11pm-1am, although most folks are theoretically asleep for at least one of the meals (the 5am-7am one for moi). We typically have our choice of three main dishes plus 4 or so veggies and side dishes at each meal, and a fruit bar and salad bar are also available. The fruit and salad bars will remain operational for another week or so (the kitchen has a special ozone refrigerator that keeps perishables fresh much longer than your typical one), but I'm told that eventually they disappear. To top it all off, there are always cookies, soft-serve ice cream, and other assorted desserts. Everything is basically all you can eat, so you can either think of it as heaven or an impending crime scene where your body fat % is the victim. I'm definitely eating a lot more here than I typically do at home (#gradstudentlife), so I've been having to exercise to compensate. But that's more of a compliment to the kitchen than a complaint, as it certainly could be much worse.
Almost every person on the ship shares a room with another person, as there are two bunks in each room. Every two rooms also shares a single shower and toilet, so you might imagine that things could get a little crowded. However, the organizers of each expedition make sure that your roommate works the opposite shift as you, so you are rarely or never in the room at the same time as your roommate and are generally only sharing a shower and toilet with one other person. I'm told that before the ship was renovated in 2008, there were actually four people to a room and still a single shared restroom for every two rooms. The ship apparently had some unsavory nicknames during that time, but things are cushy now in comparison.
The toilet system on the ship is a vacuum system much like that used on an airplane. Since carrying a two months worth of fresh water on board would be very heavy and a bit unfeasible, the boat is also equipped with a distillation and filtration system to make freshwater from seawater. The water tastes great, but it's so salt-depleted that many actually need to take vitamins or drink Gatorade once a day or so to compensate for the lack of electrolytes. Still, it's a bit funny to think that I'm drinking water so clean that I would normally have to pay for it back home.
Although the days are long and filled with collecting samples, running analyses in the lab, and writing, we still find time to step outside and enjoy some fantastic views of the sunset (or, every once in a while, of land) and stars from the ship's deck. Life is good!
Gotta get back to work, but until next time!
Cheers,
Dan
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