GLIMS Update: working group on ocean-calving glaciers (OCG)

[Jeff Kargel]

Graham,

Thanks for your terminology clarifications, to which I add some process related comments. I will respond here, but it's possibly best to get a list of people interested in these types of glaciers and eventually cut the discussion off from those who are not interested.  But it is a chicken-and-egg issue, as we have to decide what we're talking about, as you point out. So let's settle a couple definitions and why some near-beach glaciers are to be considered by the OCG, and others are not; then people can add their names to a OCG list, and we can save others from undesired mails.

>From the perspective that Bob and Tad framed, I think we're talking about glaciers that have some significant part of their terminus region touching seawater; and in addition, a fraction of those which have some fraction of their tongues floating on seawater.  Because these things are so dynamic in their terminus position, and since some of them make their own land (by dumping sediment), a glacier can easily vary in time between one whose terminus sometimes sits on a beach and dumps icebergs and meltwater on the beach and into the sea; sometimes sits on the ground but is eroded by seawater and dumps icebergs directly into the sea due in part to thermal interactions with seawater; and sometimes has part of the tongue floating in the sea.
In that circumstance, I think it matters which phase a glacier may be in, and whether it has found some equilibrium by sitting most of the time on a beach or by doing the dynamic oscillation (binge/purge; surge/waste); but these are details that don't necessarily knock a glacier off our domain of consideration.  

Where I would draw the line to not consider it, would be a land-terminating glacier that happens to advance sometimes and just coincidentally ends its advance on a beach; that would be a rare glacier, as most beach terminating glaciers will be terminating there because if it tries to advance beyond the beach it finds itself bathed in warm water, and then accelerated calving and frontal melting holds it back; that's a special case, but perhaps not uncommon and worth including in this working group's domain.  

Another near-beach experience may be effected by a glacier that wasted back from the sea, maybe after a flotation/surging event (or not), wasted far back, but debris mobilized during the surge phase finds itself dumpped preferentially where the glacier front spends a lot of its time-- as the wasting terminus approached the beach and entered shallower water and land; it can make and extend a beach (a moraine or proglacial delta).  Those are all glaciers that are strongly influenced by the big bathtub.  Because dynamical oscillations are so important for many of these glaciers, we ought not eliminate from our consideration glaciers that are temporarily stabilized near a beach.  So occasionally tidewater-calving glaciers are part of the consideration, or ought to be, because they can potentially lose most of their mass during tidewater-calving phases of their cycle.

That said, it points out the limitations of using the current GLIMS database parameters as to terminus type, since it may vary decade to decade.  Of course for sealevel, only global long-term trending is significant, but the dynamic oscillations have to be sorted out to get the trending, otherwise we may get a biased dataset.Peop[le will have to decide whether a dry-land-terminating glacier spends much time in the sea.

Is this sensible? 

--Jeff

-----Original Message-----
>From: Graham Cogley <gcogley1 at cogeco.ca>
>Sent: Mar 5, 2008 2:49 PM
>To: Jeff Kargel <jkargel1054 at earthlink.net>, GLIMS mail list <glims at flagmail.wr.usgs.gov>, Cryolist <cryolist at lists.colorado.edu>
>Subject: Re: GLIMS Update: working group on ocean-calving glaciers (OCG)
>
>Jeff - We should clarify right from the beginning what we are talking about. Are Tad and Bob concerned about "marine-based" small glaciers in the strict sense (ice grounded below sea level), or "tidewater-calving" small glaciers (not the same thing). I imagine that the adjective we want is "tidewater-calving". 
>
>There are plenty of tidewater-calving glaciers which have no part below sea level. They flow down to the beach, and there produce icebergs. Then there are the ones which stand in the water (probably the majority), and finally there are a very few with floating terminal sections.
>
>Graham.
>
>---------------------------------------------------------------------------------
>
>J. Graham Cogley, Ph.D., Professor of Geography,
>Department of Geography, Trent University,
>Peterborough, Ontario, CANADA K9J 7B8.
>
>Fax   705-742-2131
>Tel    705-748-1011-x7686
>Email gcogley at trentu.ca
>Web  http://www.trentu.ca/geography/glaciology/glaciology.htm
>
>----- Original Message ----- 
>From: Jeff Kargel 
>To: gcogley1 at cogeco.ca ; GLIMS mail list ; Cryolist 
>Sent: Wednesday, March 05, 2008 4:22 PM
>Subject: GLIMS Update: working group on ocean-calving glaciers (OCG)
>
>
>Dear GLIMS colleagues and Cryolisters,
>
>Bob Bindschadler wrote this morning:
>
>>I recently attended an Ocean-Ice Interaction Workshop at NYU.  To make a
>>long story short, Tad Pfeffer made an excellent point that if marine-based
>>ice is at the crux of near-term acceleration of sea level--and I believe it
>>is--then it would behoove the glaciology community to get at least a handle
>>on how much of the "glaciers and small ice caps" component of the cryosphere
>>falls into this category.  Tad stated that this fraction is not known--at
>>all!  I expect he's right.  It seems like a perfect tangible task for GLIMS
>>to take a stab at producing at least the percentage of non-ice-sheet
>>involved, if not some other metric such as volume fraction.
>
>Bob inquired whether GLIMS and others are ready to take on this task.  In project design, we are ready; the database includes parameters about glacier terminus properties, and people are busy assessing glaciers and ice caps, including tidewater calving glaciers, and populating the database; and in our project charter we are supposed to be looking at what Bob suggested, among other things of course.  In practice, we are globally short of manpower, but we do have people working on the analysis of these glacie
>rs, so far piecemeal.   We need something more comprehensive and consistent.
>
>To add somewhat to what Bob (and Tad) pointed out, most of the global assessments of small glaciers avoid tidewater glaciers, because of the obvious complexities, nonlinearities, and natural dynamical oscillations inherent in these complex systems.  But most of the mass balance action probably is tidewater glaciers, because of their usual large size, proximity to oceans and hence high accumulation and discharge rates, and the important influence of oceanic thermal energy.  To a lesser but important extent, 
>lake and river calving glaciers exhibit some similar phenomenology. The dynamics are in many ways similar to those of ice shelves and the ice sheets that feed them.
>
>Given the special nature of tidewater calving glaciers, and Bob's suggestion, it seems high time that GLIMS and other interested colleagues form a working group to examine the long-term trending and recent mass balance record of tidewater calving glaciers.  We would isolate long-term trending from natural dynamical oscillations, and specifically try to reach an estimation on the current sealevel contributions from tidewater calving glaciers and small ice caps.  We need more manpower in this effort, but we h
>ave to start somewhere, and I think we have critical mass to forge this group, define its charter, assemble existing assessments of these matters, and move toward an answer to Bob's and Tad's challenge.
>
>First thing is to develop a working group, then to establish its specific charter, measurement goals, reporting expectations, and timeline needed to give policy makers what they need as soon as possible.  We need more manpower, and that's money we don't have, but let's get a head start on this with what we do have.
>
>Sorry for double listings between glims and cryolists.
>
>Sincerely,
>
>Jeff Kargel
>
>    
>224.39
>X-Barracud