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<\/a><\/span>Then the ice went away, but the effects of the ice having been there are still being felt. A paper coming out next week in Nature explores the effects of deglaciation on the oceans. We can see the effects of the ice in the flooding going on right now in the Red River Valley on the North Dakota-Minnesota border. The lack of native worms in the northern regions of North America, and the survival of a number of rare plants is related to the deglaciation process. The effects of the great ice sheet and it’s subsequent melting have shaped the landscapes and cityscapes of many regions.<\/p>\nSouth Minneapolis is the largest part of the city in terms of both land area and population size. Minneapolis is called the City of Lakes (and thus, our basketball team is “The Lakers” ( … or did they move somewhere else, can’t remember … ), because of the lakes in west side of the city. If you look at a map of Minneapolis and surrounding areas, you’ll see that you can connect these lakes together between two roughly parallel lines, and that these lines indicate the outer limits of an ancient river channel. The river channel is still very much in place, and if you get down on the ground you can see where the sides of this channel are even where there are no lakes. The lakes are simply spots within the channel that were filled with more ice than sediment as the glaciers melted away. When the ice melted, a depression was left behind, and that depression is now a lake.<\/p>\n
This explains why most of the lakes around here, most of which were formed from ice melted in the glacial ’till’ (as the stuff is called) are round. Imagine a concentration of big chunks of ice of any shape in one area below the ground. Maybe they are 30 feet to 200 feet below the present surface. It takes them forever to melt, but eventually they do and even if the void left behind is filled with water, the sediment collapses into the void. Now, think of this void as the lower part of an hour glass. as the sediment from above sifts and pours down into the void, the space that is above the passage way into the void is more or less unformly empties of its sediment, which means that an odd shaped void down deep is displaced and becomes a globular (round, from the top) shaped void above. A rounded circular depression in the landscape, which in turn becomes a lake.<\/p>\n
If you take a broader view of the region, you can see that there are segments of ancient river channels all over the place, and if you start connecting them together, you will see that there is no way that these channels can be matched up to be the single channel of some ancient river. Rather there is a web-like network of channels everywhere. At any given time in prehistory, one or two rivers meandered across this region using some subset of channels.<\/p>\n
If you remove all the glacial sediment and leave only the channels, what you would actually get is a landscape consisting of buttes and mesas separated by u-shaped valleys. It would look roughly like the badlands of the Dakotas.<\/p>\n
One of these ancient channels (as discussed here<\/a>) is the large recent course of the Warren River, and it is the nature of this valley’s formation that contributes to the modern day flooding we see in the Red River Valley, which occupies part of this ancient water route.<\/p>\n Getting back to the peer reviewed paper at hand.<\/p>\n This is the abstract from the paper, and I’d like this abstract to serve two purposes:<\/p>\n Rivers are the dominant source of many elements and isotopes to the ocean. But this input from the continents is not balanced by the loss of the elements and isotopes through hydrothermal and sedimentary exchange with the oceanic crust, or by temporal changes in the marine inventory for elements that are demonstrably not in steady state. To resolve the problem of the observed imbalance in marine geochemical budgets, attention has been focused on uncertainties in the hydrothermal and sedimentary fluxes. In recent Earth history, temporally dynamic chemical weathering fluxes from the continents are an inevitable consequence of periodic glaciations. Chemical weathering rates on modern Earth are likely to remain far from equilibrium owing to the physical production of finely ground material at glacial terminations that acts as a fertile substrate for chemical weathering. Here we explore the implications of temporal changes in the riverine chemical weathering flux for oceanic geochemical budgets. We contend that the riverine flux obtained from observations of modern rivers is broadly accurate, but not representative of timescales appropriate for elements with oceanic residence longer than Quaternary glacial-interglacial cycles. We suggest that the pulse of rapid chemical weathering initiated at the last deglaciation has not yet decayed away and that weathering rates remain about two to three times the average for an entire late Quaternary glacial cycle. Taking into account the effect of the suggested non-steady-state process on the silicate weathering flux helps to reconcile the modelled marine strontium isotope budget with available data. Overall, we conclude that consideration of the temporal variability in riverine fluxes largely ameliorates long-standing problems with chemical and isotopic mass balances in the ocean.<\/p><\/blockquote>\n If you read that, your head probably hurts because it is a typical scientific abstract written to not be understood by the average person. First, I want to tell you briefly what it means, then I want to pick out a few sentences and hold them up as reasons that that authors who wrote this and the editors who let it pass should be flogged. (Flogging is British, right? This is Nature. So, right, flogged.)<\/p>\n What it means is this: The elements that are dissolved in the ocean change over time more than we would expect if this was simply a matter of the hard parts of the continents slowly eroding into the ocean, and the ocean getting rid of some of these elements when they settle to the bottom of the ocean or go somewhere else. It turns out that after a glacial period is over and the ice goes away, there is extra chemical stuff eroding into the ocean because the glaciers ground up more of the rock than would normally be eroded to contribute chemicals to the ocean. Interesting. Simple. Important. Not hard to understand.<\/p>\n But this is hard to understand:<\/p>\n In recent Earth history, temporally dynamic chemical weathering fluxes from the continents are an inevitable consequence of periodic glaciations.<\/p><\/blockquote>\n Let’s break it down.<\/p>\n “In recent Earth History..”<\/p>\n This is a paper about the earth. And history. That this is Earth history and recent tells us nothing but adds mystery. This is nota mystery paper. Give dates. Such as, “During the last two to five million years” ..<\/p>\n “temporally dynamic chemical weathering fluxes”<\/p>\n OMG give me a break. Temporally = over time. Dynamic = changing, variable. Fluxes = changes. The word “chemical” in a paper about “elements and isotopes” means nothing. Oh, and by the way, isotopes are elements… no need to use the extra words.<\/p>\n Try: “Over time, changes in weathering”<\/p>\n “are an inevitable consequence of periodic glaciations.”<\/p>\n That’s OK, but it is really just hoiti toiti language. So, this:<\/p>\n In recent Earth history, temporally dynamic chemical weathering fluxes from the continents are an inevitable consequence of periodic glaciations.<\/p><\/blockquote>\n … would be readable and more literate if it was dynamically fluxuated into this:<\/p>\n During the last 2-5 million years, changes in weathering from the continents happened because of periodic glaciations. <\/p><\/blockquote>\n Is that so hard?<\/p>\n Here’s a half dozen more bits of the abstract.<\/p>\n … To resolve the problem of the observed imbalance in marine geochemical budgets, attention has been focused on uncertainties in the hydrothermal and sedimentary fluxes. <\/p>\n … the physical production of finely ground material at glacial terminations that acts as a fertile substrate for chemical weathering. <\/p>\n … we explore the implications of temporal changes in the riverine chemical weathering flux for oceanic geochemical budgets. <\/p>\n We contend that the riverine flux obtained from observations of modern rivers is broadly accurate, but not representative of timescales appropriate for elements with oceanic residence longer than Quaternary glacial-interglacial cycles. <\/p>\n … Taking into account the effect of the suggested non-steady-state process on the silicate weathering flux …we conclude that consideration of the temporal variability in riverine fluxes largely ameliorates long-standing problems with chemical and isotopic mass balances in the ocean.\n<\/p><\/blockquote>\n How would you rewrite these?<\/p>\n Vance, D., Teagle, D., & Foster, G. (2009). Variable Quaternary chemical weathering fluxes and imbalances in marine geochemical budgets Nature, 458<\/span> (7237), 493-496 DOI: 10.1038\/nature07828<\/a><\/span><\/p>\n","protected":false},"excerpt":{"rendered":" A very large percentage of the earth’s land masses were covered by glacial ice during the last glaciation. Right now it is about 10%, but during the Ice Age it was much more. Enough of the earth’s water was trapped in this glacial ice that the oceans were about 120 to 150 meters lower than … Continue reading The Ice Ages Matter (Even Today)<\/span>
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