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[Music]

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thank you uh so yeah I'm Sarah Miller

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I'm working with Professor Brittany

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Schmidt at Cornell University and I am

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working to build a global circulation

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model for the ocean at Europa

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um so before we move on I wanted to kind

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of point out the cover image I chose

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which is primarily because I thought the

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colors made for a pretty PowerPoint

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theme and secondarily because it shows

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some interesting kind of structures that

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exist on the ice crust on Europa so as

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you can see it's not a smooth ice

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skating rink it's a very interesting and

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geologically active Zone which hints

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that probably the interior is a dynamic

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and very interesting place to study

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which is what I'm going to talk about

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next before I dive into the science I do

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want to take a moment to thank my team

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and kind of the people who have helped

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me bring my understanding

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um in this field up so I have a

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background in fluid dynamics and

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aerospace engineering which I'll talk a

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little bit about throughout this talk

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but these people have been really

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instrumental in kind of working with me

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on the planetary aspect as well as my

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funding sources through an NSF grfp and

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a NASA finest in an Amelia Earhart

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fellowship and some wonderful people who

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support this work

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okay so as I mentioned uh Europa has a

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very interesting surface and it hints

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that there is a dynamic ocean interior

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and I think that the ocean circulation

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the physical oceanography piece of this

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puzzle is a really interesting one in

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terms of habitability because when we

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look at Earth's ocean

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um the transport of heat and salt and

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nutrients throughout the ocean column is

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really what sustains our biosphere so I

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think it has really interesting

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habitability implications on other

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planets as well and specifically I want

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to narrow this down even further the

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region of our ocean that separates the

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glacial glacially covered parts of our

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ocean from the liquid layer that ice

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ocean boundary layer is really

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instrumental in setting far-field ocean

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properties so that tiny boundary layer

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region between the ice and the ocean

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actually has an outsized effect on

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affecting Global Mass Water mass

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transport and so I think that's very

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much worthy of intense study in the

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modeling realm for Europa

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so I'm not the first person to attempt

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to build a global circulation model for

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Europa

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um but the the state of the field is

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really kind of Divergent so um models of

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Europa generally fall into one of two

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categories depending on kind of how you

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set your boundary conditions and really

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how you set up this ice ocean interface

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mathematically so usually there's kind

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of an outsized effect of either the

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rotation driven or buoyancy driven so

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kind of temperature salinity gradients

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in the model and the results are very

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different so Global circulation models

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exist they usually fall into one of

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these two categories and they do not

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agree with each other now if we look at

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terrestrial Ocean Models on the other

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hand they look very different and that's

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because they've had a lot more

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scientific Manpower in years of study

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and actual data so how nice for them so

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their models are very sophisticated

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compared to what we see in planetary

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Ocean Models

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that being said there are still kind of

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parts of Earth's ocean that we don't

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understand so it's very much ocean

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modeling is an active area of research

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and there's still some mechanisms that

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remain poorly constrained which is

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really humbling to think about doing

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this on a body that we have zero data

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for and know a lot less about

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but I'm going to try anyway

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um so let me introduce you to the tool

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that I'm using so I'm using the MIT

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General circulation model so it's a 3D

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circulation model that employs the full

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non-hydrostatic incompressible navier

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Stokes equations

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it also has some really interesting and

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very useful packages for Europa so an

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ice shelf package

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um

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a deep convection package which is

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really helpful because Europa unlike

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Earth has a really deep ocean compared

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to its planetary radius and that is

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important when you're talking about

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large scale flow features so I won't

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kind of dive into the nitty-gritty it's

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written in Fortran

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um so if you're a modeler you're

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probably just cringed uh but yeah it's a

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very powerful very useful tool

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so there's lots of knobs that you can

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turn within this model and I'm working

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on turning kind of all of these through

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sensitivity studies throughout my PhD

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but what I want to focus on in this talk

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is the role of topography underneath the

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ice shelf so in this case I'm talking

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about both the small scale topography so

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surfness roughness surface roughness of

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the ice which affects things like

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turbulence in the boundary layer as well

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as large scale features on the ice that

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can form large scale flow features now

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you might be thinking like why would a

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turbulent boundary layer affect global

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ocean circulation

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and specifically habitability for this

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interest and I want you to remember that

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the ocean time scales operate a lot

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faster than planetary time scales and

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that could be an important link for a

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habitability argument

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so quick review of kind of boundary

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layer of physics

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um I took out the full equations because

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they're pretty ugly and I just have

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these like nice kind of simplified

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relationships that I want to discuss

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um so I'm using kind of a widely adopted

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parameterization called the three

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equation parameterization it's very

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creatively named and essentially it's

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just looking at this fluxes those are

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those Q values between a solid ice shelf

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which is fresh water or fresh ice a

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mixed boundary layer region and then the

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mixed layer the liquid ocean

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so we're looking at kind of the three

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unknowns in these equations are the

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temperature and salinity of the boundary

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layer as well as a melt rate or MDOT

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which is negative if it's melting

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positive if it's freezing and that's

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kind of how we're constraining the phase

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change that's happening at this region

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so I'm using a model that's um

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kind of an ongoing International effort

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within the MIT GCM Community to uh

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model this kind of physics

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um for Earth's ocean and so this is a

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simplified version of that map and so

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it's a two equation parameterization

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that's assuming the salinity of the

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boundary layer and the mixed layer is

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the same

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um current research and kind of more

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recent results since submitting this

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abstract I've been able to like use the

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three equation parameterization but

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those graphs are still pretty ugly so

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maybe next at gradcon

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um

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yeah and kind of one other thing that's

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very common on Earth but not a great

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approximation for Europa is that often

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in Ocean Models the pressure dependence

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of density is approximated by depth

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dependence I mentioned that europa's

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ocean is a lot deeper than Earth's so

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this is something that I've removed as

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well because I think

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no longer holds for europa's ocean

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so I mentioned it's probably not like a

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flat ice skating rink under europa's eye

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shell we don't know what it looks like

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but it's probably not that beautiful and

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simple

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um it's probably not this beautiful and

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simple either but to start with to kind

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of demonstrate some of the flow features

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that might develop with ice shelf

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topography here's like a very simple

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ramp that I'm introducing so it's not a

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global model quite yet it's just a

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rectangular domain starting at a fixed

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initial

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temperature

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um

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and we're going to introduce a heat

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gradient and a flow through ice melting

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and see what develops

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so we're seeing some already just with

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very simple geometry interesting and

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kind of recognizable flow features so we

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see the development of what looks kind

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of like a western boundary current on

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the left and an ocean gyre on the right

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and these are happening because there is

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melting happening at depth so if you

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remember the phase diagram of water

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there is a pressure dependence on the

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melting point of ice and so we see

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melting happening on the bottom of this

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ramp and then as the fresh waters Rising

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along the Melt water the ramp it's

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circulating and that's creating a

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circular flow feature this dryer

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so we have on the left these are just

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stream functions the barotrope extreme

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function and then the right and

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overturning stream function just in a

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couple different directions

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so maybe more importantly uh

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the Melt rate what's happening so we're

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seeing both regions of melting and

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freezing The Contours got a little dense

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for the melting so I just kind of

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outlined that where that's happening

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there but that's happening um kind of as

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the warmer Ocean mixed layer water is

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interacting with this Frozen ramp

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and so we see that kind of

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um already just very simple geometry

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there's lots of Dynamics happening

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there's freezing there's melting there's

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flow features

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um

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but this is probably not very realistic

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maybe more realistic is something like

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this so

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this is a almost Global

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um topography that I stole from what

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Earth's ice shelves look like I cut out

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the poles because of convergence issues

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and it's a pretty coarse resolution but

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it still captures a lot of the large

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scale flow features that we see on Earth

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as well as some turbulence and mixing

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events effects from small scale features

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that are missing and so

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I think it's really important to think

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that like when you're modeling

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um

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heat transfer like your grid resolution

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is really important so the size of your

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grid cell in your model affects kind of

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how quickly heat is transferred through

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your ocean and so this is really too

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course to understand

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um

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what's happening in turbulence and

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Boundary layer effects so I'm

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kind of

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accommodating that in the model by

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modifying the MIT GCM to have like

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spatial grid remeshing so I'm slicing up

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the grid cells

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so that I can have melting and freezing

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happening within a single model run

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which is not kind of the standard

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configuration

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within the boundary layer so this has

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been kind of very helpful in

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understanding

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um

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turbulence and more quick time scale

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now this is kind of one of several

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things that needs to happen to have a

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more realistic ice shells like greater

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spatial grid density in the boundary

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layer

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um

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there's also but even so you know it's

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not going to be a simple ramp

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um

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there's other things to introduce like

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salt different heat and salt transfer

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coefficients

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um

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a mushy layer there's interesting work

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that's being done by this on this by

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Jacob buffo if you want to look at his

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work

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um

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so in my model currently the ice is

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assumed as a completely fresh water

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layer that's probably not the case there

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might be zones or brines and interesting

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kind of pockets of heterogeneities that

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will affect these processes but this is

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kind of all just taking steps to like

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introduce more realistic features into

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an ice shell model and then look at the

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global circulation effects of those

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features

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so kind of to kind of wrap up this

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little bit that I've discussed

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um

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terrestrial models I think can be very

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valuable in the planetary Community

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within those models specifically I think

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there still needs to be a lot of work

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done on the ice ocean boundary layer

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which is what I've been focusing on this

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past year of my PhD and the potential

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impacts for habitability of this kind of

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great uh resolution on an ISO student

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boundary layer could be very important

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for habitability

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all right and I'm happy to take

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[Applause]

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so if you are assuming uh so with the

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mushy layer you know like a slurry for

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instance is the Assumption of uh

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incompressible fluid still valid and

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does that change that makes never Stokes

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much more complicated right so how would

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that really affect the your modeling

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would you have to change some things or

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yeah no that's a really good question so

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um realistically yes you would change uh

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the kind of forcing equations so the

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model as it currently runs it assumes

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that um

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kind of backing up a little bit the

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equation of state of seawater is a

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linear function of salinity so if you

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introduce something like a brine

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it's removing that kind of linear

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assumption that said like the model as

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it currently stands it does have a solid

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ice layer so it doesn't look at brine

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Pockets or mushy layers yet

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um

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if you wanted to do that I do think that

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yeah you'd need to change the equation

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of State at seawater locally yeah to

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accommodate those and what about the

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incompressibility assumption I think

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that's a small enough one where if

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you're looking at the effects on

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overturning in flow it wouldn't have an

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effect but it would be a very cool

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sensitivity study so it's a good

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sorry a really ignorant question so

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Europa it seems like there's a

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very kind of notice

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notice gradient is that just due to

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pressure kind of like what what's the

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middle of Europa oh interesting question

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okay I think I have

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um a backup slide that might help so

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yeah so the mechanisms that are kind of

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important for Europa Heating and what's

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sustaining the ocean are like tidal

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heating that it bottom heating from

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residual heat of formation internal heat

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if there is this Dynamic eye shell

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that's freezing and melting like I think

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it is then you have heat fluxes from

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freezing and melting

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um

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yeah so there's a lot going on

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um the kind of Weights of these effects

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is still very much unknown and so that's

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why I'm really trying to use

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observations from Earth so for instance

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I'm using like turbulent turbulent

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transfer coefficients of freezing and

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melting from Antarctic field studies to

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kind of influence this model but yeah

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it's really like there's a lot going on

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so it's really kind of the challenge is

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trying to figure out which one is

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driving

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um

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okay we have time for one more question

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Taylor plattner at Georgia Tech great

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00:14:52,730 --> 00:14:50,699
talk Sarah

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um you were talking about Brian Pockets

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to like make it the model more realistic

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did you have do you plan on doing that

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with your model and have they done it on

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00:15:06,710 --> 00:15:04,199
earth like with like Earth models have

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they even thought of like incorporating

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bride pockets

405
00:15:12,230 --> 00:15:10,320
yeah it's a good question so the answer

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is like no most

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um like

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glacial models and Earth Global ocean

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00:15:20,269 --> 00:15:18,660
circulation models don't include brine

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Pockets because on Earth those are more

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seen in like Lake environments or kind

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of like the like hyper saline lakes and

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Flash bows and lakes that like Jacob

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works on

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um

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they might Europe as a yeah different

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00:15:32,990 --> 00:15:32,220
conditions though

418
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um

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and so they could exist there so at most

420
00:15:40,310 --> 00:15:37,800
I think I would do a like a case study

421
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on what would happen if Brian Pockets

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exist so it's something I'm working on

423
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now

424
00:15:45,650 --> 00:15:44,040
um but it's not something I'd include in

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00:15:48,110 --> 00:15:45,660
every run because it's just still very

426
00:15:49,310 --> 00:15:48,120
much an unknown yeah I was going to say

427
00:15:51,410 --> 00:15:49,320
that was kind of like a loaded question

428
00:15:55,430 --> 00:15:51,420
but I was curious no it's a good

429
00:15:55,440 --> 00:16:02,420
thank you so much for the time

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00:16:10,750 --> 00:16:08,949
[Music]