good evening i need vonne step for science for the public and i welcome you to contemporary science issues and innovations tonight we learn about the relationship between glacial melt and the earth's climate history these historical melting patterns in the information from their deposits are very important resources for modern climate science are distinguished guest is jack ridge professor of geology and chair of the department of earth and ocean sciences at tufts university dr ridge has received prestigious awards and is a fellow of the geological society of america tonight he shares with us his expertise on glaci geology especially what glacial sediments call vars reveal about climate change over centuries and additional kinds of information such as when the ancient  possible or not in some areas i should mention the dr ridges far website is an excellent resource for students and teachers and the general public it is a great pleasure to welcome professor jack ri you and i wonder if we could start by getting a little background about glaciers the reason i ask is that there seems to be a lot of interest related to climate science  up is a picture of the sit in a glacier in alaska when we refer to a pile of ice and snow that is a glacier it has to have a couple characteristics one it has to be the result of the accumulation of snow and second it has to show evidence of movement so glaciers move by sliding across the land surface but when you stack up snow and ice to a great thickness as occurs in greenland during an article  ice at the bottom is under enough pressure to do form under its own weight so the glaciers moving across the land surface and we see the results of that today we see scratches and grooves on the land so yes and we see all the deposits on the land surface that were brought here by the ice so the picture is this is certainly place here in alaska all glaciers have high elevation areas where snow falls on the ice sheet and it doesn't melt in the following summer so it continuously stacks up to the point where the ice starts to move and it moves to places of lower elevation where last winter snow entirely melts off and older ice melts off so you're producing melt water a glacier that's in balance will have as much snow falling on it as melt water leaving oh i see so but the problem is right now we don't have that balance where  losing mass they're delivering more melt waters to the rivers and lakes that are in front of them and eventually it ends up in the ocean then they're receiving as you know fall so we have a situation where the glaciers are getting smaller right now  as a result of you know the warming of the climate and that is one reason why there's a great interest in them now that's a kind of an acceleration of this ok in terms of over the history of the earth  relationship between glaciers and climate yes could you give us a little bad ground about that to please yes so north america is a good place to talk about this so for about the last two and a half million years we've had periods of time that are dictated by cycles in the earth's orbit where we have cooler conditions we receive less sunlight and as a result snow and ice starts to accumulate at higher elevations and the result is that we have the growth of ice caps starting about two and a half million years ago in north america had an ice cap grow on it those periods of time that we call glaciations are followed by warmer periods that we call interglacials ok and so those are periods of time when we receive a little bit more sunlight and the ice sheets collapse and they melt the water goes back into the ocean when we have a glacial period a lot of the water that's in the oceans actually stored on the lancer for so we have a lower sea level so that's been going on for about two and a half million years and right now we happen to be in an interglacial period a relatively warm period if we were to go back twenty five thousand years ago and back to boston  would be under a considerable amount of ice at that time maybe a thousand meters well so that didn't delta house or through north america was did that glacier go the north american glacier of dirt put down at the margin of the glacier so all of the all the rest of the wing was completely under the yes and the glacier spread out on to the continental shelf east of of new england so there was  considerable thickness of ice here and that margin goes across right through new york city in fact right across that an island in new jersey and pennsylvania back up into new york state and back out in new york state across northwestern pennsylvania  a big thing we're concerned about now is how they came to lands now and how they move we want to know their velocity and we want to know how modern melting influences that so there's a lot of work for instance name done in greenland on that type of thing  we're also worried about the antarctic ice sheet the volume of ice there is tremendous if we were to melt all the places in the world sea level would rise about sixty five meters if we were to go back to the last ice age and put all of the ice pack on the land surface sea level would be about one hundred thirty meters lower than where it is today so the health of glaciers right now is something that basically control sea level change and glaciers are is this present climate change period markedly different in terms of the acceleration of the melt or whatever while the glaciers in places like alaska in greenland are probably receding as fast as the glacier did at the end of the last ice age you know that whole way sure was much bigger in the climate was colder at that time as the glacier was receding but the glacier was also much further south so eventually what happens is the climate starts to warm up and the glacier gets out of equilibrium and starts to melt very fast so in my work i've been able to document in the connecticut valley a period of time where the glacier receded at about two hundred fifty to three hundred meters a year so some glaciers are receding that fast there usually glaciers that are ending in water and icebergs running off the ice that helps facilitate the recession or the retreat of the glacier but the time in terms of the acceleration rate there no it's a rate that was matched back to the end of the last and i said certainly that was on what's unusual about that time period is that climate system operated differently when there were glasses on the planet the glaciers change to things in a big way they along with the growth of glaciers we get the reflectance of the glacier surface putting radiation ocean circulation can change lead to some extremely abrupt changes in climate where over a period of a few years meaning your temperature might drop six or seven degrees centigrade and at the end of that rise six or seven degrees centigrade very abruptly i see so the climate is during an ice age is much more erratic and prone to much larger fluctuations that we see now and that's not to say that global look at so far and my work what i'm trying to do is study the last ice age and piece together what the climate was like during the last ice age not necessarily determining exactly what the temperature was right know significant they called it in today because the edge of a glacier was here in the yeah there's no question about that but we're trying to figure out what the pattern of climate was from the time the glacier reaches its maximum extent and as it melted so one way to look at that would be that the glacier would just start to melt backwards and the climate would slowly warm up and the glacier would recede and we know for a fact that that's not exactly what happened wow that there were periods of time w ice would recede rapidly and then it would get cold again it would read vance maybe not to the extent that it had reached previously so i like to say that the glacier had a sort of a nervous and jerky recession  just incidentally there seems to be interest in this you may know something about it that they had set back the date when humans arrived in north america and i thought i'll just have to you about that because people in your business can probably say whether they could have inhabited and that might be very on even the different areas of the north america so in that particular situation what was don't really know when the bone wisco will sculpted so i think it's an interesting find yeah but i think the jury is still out on what that actually represent if it doesn't fact represent humans being here at one hundred thirty thousand years ago that would be a monumental change in the way we think about things you would that would be the sort of thing that you could sort of verify  interesting point that you know it's a very ancient ball but i mean if you found a mammoth bone and men with guns were very valuable to those early people the guy used them to make tools it would be something that they would use regardless of how old it was it would have to be pretty well preserved but you know it could be a very old bone sculpted by somebody that would be much more on this isn't exactly exactly which would make lots of sense but the other thing is would you yes which did roam along the edge of the ice sheet they lived in an arctic climate but there's also colombian mammoths for instance that are found in the library at targets in los angeles so they lived in a warmer climate and they lived down through central america so they were they were like you know of yeah yeah you know they weren't hairy like well in mammals right i see so they could have easily been here long before humans arrived or whatever well thank you for that but  since there is so much apparently in reading these valar that you're going to tell us about that there's you can really we construct a history of the climate and of the earth apparently from that glacial lakes which is what we're going to be talking about but they form in a lot of other environments any place where sediment is put down differently in the summer versus the winter so monsoonal climates would be a would be situations where you might have virus where there's a rainy season and a lot of runoff and sediment pours into a lake and then there's a season where you know a really fine sediment settles and we have a slightly different layer put down during that time of the year but that would give us a and it's showing the major glacial lakes that were in front of the receding ice sheet is receding from the yellow the orange line down at the bottom and yet where its maximum extent is it recedes like a windowshade van pulled up my answer and as it does that in a few places there are lakes in valleys like the merrimack valley in the connecticut and the hudson valley and those lakes expand at the front of the  and they probably had icebergs in them and everything with them like places in alaska and you know the ice recedes in the northern new england these lakes expand and get much longer and they last a long time so they're receiving se being put down across the floor of the lake so when i say course i mean i've seen and in silt but when the winter rolls around the melting stops and what happens is that all of the really fin particles that are in the way the clay particles them settle and they produce a distinct winter layer and that's what allows us to find bars are they ok all right and we'll see that with so yes what we do is we go to places where there were so this is actually a core from a south windsor connecticut ok so what we did here is we prepared the course so that you can see the individual winter and summer layers so we take that core and we split it in half and we shave it with a knife for a razor and then we slowly let it slowly dry and the clay beds retain their moisture so they remain dark in the silt and in sand bags that are positive and summer get lighter in color of the dark band of the clay bed it would feel like grease ok not very very fine said yeah yeah so this is in this section of course was a scale over on the left we have an centimeters each one of those dark bands is a the melt season of the summer may have only been ninety or one hundred twenty days long when they were melting conditions i see so that can change if one year is cloudy or or slightly cooler there won't be as much melting there won't be as much sediment put into the light so every year is going to be different and that's basically recording differences in weather weather patterns from year to year ok but over the long term what can happen is over centuries you may go through a warm period with a virus or generally secor and then a cool period where they're generally thinner and we can see that in these records in these cores so this is a record of the climate over a very long period of time it can be so we have our we have a virus in the connecticut ballot it's over fifty six hundred years long so for fifty six hundred years we can sort of track what the climate was doing when i was warm and cool how many yes so what we have to do is we have to correlate the course that we take from different parts of the valley and put together a long record does it tell you anything else from a geological standpoint like the mineral make up or anything to see if anything it well the mineral make up of the virus will give them different colors so when we are down in southern connecticut and we're investigating barbs they're red because there's red sedimentary rocks that got ground up by the glacier and that's the color of the sediment that ended up in the lake and it would have been pretty strange thing if you were there during the last ice age there'd be the glacier in the lake and the water in the lake would look red because goodness sake because of all the red shale that was ground up by of ice and also that traditionally viral records have been used as time scales because you have an unbelievable resolution of time so this is from the last ice age those pictures that you saw there are from barbs that are about seventeen thousand years old very clear yet so that's seventeen thousand years ago and you can see individual years that's yeah yeah it's illegal reza right right but some bars when i think are you can see events during the summer so you can see a rainstorm advancer big all other good business of study the glacial history look at all kinds of information that these things leave us from the distance past very accurate once you know so there's there's four things that we can do with the bars the first is that we can set up a time scale and we can we can measure how fast the glaciers are said i said before the glaciers receding at three hundred meters a year i know that because of the annual layer counts that we do from the southern end of the bal yeah very accurate and so that's one thing that we can do so the patterns of thickness change that we see in the virus also tell us something about what's happening to the climate we can see abrupt cold events where the virus are relatively effective and then they get very thin all of those we can see when drainage events occurred so if there's a small lake in a tributary valley and it's released and it flows into the main valley produces a flood event and we can see th plants that don't live in anymore and we can tell exactly what the vegetation was like on the land surface the other thing that we found in and a colleague of mine a tough jacob banner is an expert witness is we find evidence of vertebrates and also invertebrates that we're living on the floor of the lake so when they live on the floor of the lake they crawl across the settlements or if we're at an outcrop or an exposure we can peel apart the beds and see their tracks and trails so you can see the tracks and trails of all kinds of things like name a toad worms an insect larva a and small crustaceans but the big find that we had about fifteen years ago was we found the trails left behind by fish swimming across the floor the way from that time on that time period so you can tell one fish first arrive in the connecticut valley and so at least two different species probably an arctic char and seems like it's extremely accurate you have to you can narrow with modern equipment and so on to ways of analysis you can get so it's very precise in terms of you know what year you're virus was ten years older than i very precisely right exactly but the biological data yeah really give you a year and then you can handle that that's very interesting that's very interesting well you probably spend a great deal of time in lot of information at this time is it a good field for young people to be getting into at this time well i think in general glacial geology is a pretty important thing because the soils that we have on  land surface are primarily glacial sedum our groundwater resources in many places come from glacial deposits and especially in valleys that are filled with sand and gravel left behind by you know deposits put in shallow for the most part so when the glaciers pumping all the sediment in they fill up with sand and gravel with permeable material that is now you know basically filling valleys across new england and there's lots and lots of water wells that are in those palms and it represents an extremely important groundwater resource so understanding how they're deposited right and what they're geometry is in the subsurface yes is very important to understanding that resource right so this is really a critical part of earth science in general at this time and a good time to be in this field i'd imagine you know i think so right i guess that you will be going out into the field here soon is that the can said the summer do you have a few projects that actually will probably end up in new york state for a week and then in the connecticut valley for a few weeks and then right here in the middle sex sells for and not studying viruses but stuff that rocks so we talked about how fast glaciers were receding in places like alaska these are images from the national snow and ice data center and i recommend that peterson glacier it's bell p e d v r not pay and where is it it's in alaska so there's a picture from one nine hundred seventeen you can see the margin of the glacier and there was a glacial lake in front of that glacier at the top  top and in the bottom is a picture in two thousand and fifteen years as meadow which is the old floor of the lake and way off in the distance is the margin of the peterson glacier today and it's receded you know kilometer time right a man they really started to recede quite rapidly yes and this is specially true in alaska it's also true in greenland yes a good bit of alarm but now yes so the antarctic is a little different because it's a polar glacier it's own extremely cold climate yes and it doesn't have quite the same response to climate change the one place in antarctica is responding a little bit like the other glaciers which are warmer climates is in the antarctic peninsula the peninsula is right across from south america and there were saying you know ice shelves breaking up