PROJECT SUMMARY: Collaborative research: Land and ice sensor network revitalization and
collection of exposure age samples in the Larsen B embayment
Introduction
This proposal aims to strengthen the infrastructure of sensor networks across the northern Antarctic
Peninsula (nAP) to (i) allow investigation of decadal trends in the regional response of the cryosphere to
regional warming; (ii) observe and quantify climate and weather patterns responsible for the changes; and
(iii) measure the ongoing and future impact of ice mass loss on crustal rebound. The existing sensor
network has made major contributions to understanding the detailed meteorological patterns that drive
changes in accumulation, ablation, and surface melting leading to ice shelf disintegration (Cape et al.,
2015). The stations provide weather (13 sensors), firn temperature profiles (3 sites), precision GPS (12
sites), and daily images (3 sites) uploaded by Iridium. Passive seismic data (3 sites) is stored at the
stations.
The station network is installed in one of the fastest-changing areas in the polar regions, the northern
Antarctic Peninsula. The region has experienced rapid regional warming (Skvarca et al., 1996; Vaughan
et al., 2003), specifically a ca. 2.5°C increase in mean annual temperature between 1940 and 2010. Two
major ice shelf disintegrations have occurred in the region, the Larsen A in 1995 and Larsen B in 2002
(Vaughan et al., 1996; Doake et al., 1998; Rack and Rott, 2004; Scambos et al., 2003). Subsequent
glacier acceleration has resulted in high rates of mass loss (Rott et al. 2002; Rignot et al., 2004;
Shepherd et al. 2012) and elevation change (Scambos et al., 2004; Scambos et al. 2014). Consequently,
the region has seen dramatic rates of uplift, predominantly from elastic rebound, exceeding 1 cm yr -1 over
a significant area. A remnant section of the Larsen B Ice Shelf, situated in the Scar Inlet area (we will
refer to it as the Scar Inlet Ice Shelf here) remains intact, but shows signs of increasing instability.
Thus, the Scar Inlet Ice Shelf and its two major feeder glaciers, Flask and Leppard, may experience a
sequence of disintegration, glacier acceleration, ice mass loss, and isostatic rebound similar to the events
of 1995 and 2002. It has steadily evolved towards higher flow speed, increased crevassing, weaker shear
margins, and some thinning (Khazendar et al., 2015; Paolo et al., 2015). Our installed sensor network,
coupled with remote sensing data provides an unmatched opportunity to observe a major transition that
will shed light on both the causes of past similar events and the likelihood of future similar transitions
elsewhere in Antarctica. The aim of the present proposal is to ensure that we can realize this opportunity.
In addition, we propose to leverage our proposed logistics plan to expand the geologic record of preinstrumental glacier change in the Larsen B region. Specifically, we propose to visit ice-free areas that
past reconnaissance work shows are suitable for cosmogenic-nuclide exposure-dating of glacial drift. This
would build upon earlier work from the Larsen A/Prince Gustav Channel region (see Figures 8-9; Balco et
al., 2013) and complement marine sediment core records in the Larsen embayment (Rebesco et al.,
2014; Domack et al., 2005; Evans et al., 2005), with the aim of identifying and quantifying past ice shelf
and glacier changes that took place in at least part of the Larsen embayment during the Holocene.
Significant results from operation of the existing sensor network
Installation of the LARISSA cGPS, passive seismic, and AMIGOS network began in April 2009 and the
first phas was completed with installation of the AMIGOS on Cape Disappointment in November 2011
(Table 1). The network was originally designed for 3 years of data collection, but the significance of the
initial GPS measurements of crustal rebound justified an extension to 2017 and the addition of the Spring
Point and Prospect Point cGPS sites in 2013 and 2014. This was supported via a small grant from NSFPLR (see current and pending for PI Domack).
In addition to the crustal rebound data, additional observations of weather, surface melting, accumulation,
and glaciological data have yielded important information for understanding climate patterns related to ice
shelf disintegration, tidal amplitude on the ice shelf, calving and ice front evolution, and glaciological
instability that may presage the break-up of the Scar Inlet Shelf. Highlights include the following:
1) observation of the highest known rates of vertical crustal motion in Antarctica (i.e. Foyn Point at
about 1.8 cm/year; Nield et al., 2014);
2) inference of very low mantle viscosity beneath the nAP from a crustal rebound model (viscosities
of about 6×1017 to 2×1018 Pas);
3) resolution of the spatial pattern of crustal rebound in response to mass loss of tributary glaciers
following 2002 collapse of the Larsen-B ice shelf (Thomas et al., 2011; Nield et al., 2014);
4) refinement of GRACE estimates for GIA and thus current mass balance for the nAP (Ivins et al.,
2014);
5) observation of the highest surface temperature ever recorded in Antarctica (+18.7°C at Foyn
Point on March, 24, 2015) and images of coeval surface melt effects;
6) estimates of seasonal changes in snow and ice loading from cGPS data (Domack et al., 2015);
7) measurement of a 10% increase in the speed of Flask Glacier and Scar Inlet Ice Shelf between
2010 - 2015;
8) first surface mass balance measurements from the area, showing a gradient from ~3 m w.e. at
the Bruce Plateau ridge summit to near-zero on the Scar Inlet Ice Shelf (Berthier et al., 2012;
Scambos et al. 2014);
9) archive of AMIGO camera images documenting calving, retreat, surface melt formation, and
increased crevassing of the Starbuck and Scar Inlet ice shelf fronts;
10) information on the regional climatology of foehn events and their potential importance to ice shelf
disintegration (Cape et al., 2015);
11) thermistor profile measurements that constrain nAP surface temperature change for the past
~200 years (Zagorodnov et al., 2012).
Several additional results are in preparation that are likely to have a significant impact, including: (i)
analysis of the synoptic weather pattern and events of the record warm air temperature occurrence in
March 2015; and (ii) an coupled meteorological and image analysis study of the local evolution of the
Scar Inlet Ice Shelf AMIGOS site, and the ice front as seen from Cape Disappointment. In addition,
although seismic data have yet to be retrieved, we anticipate that these will be important in understanding
calving dynamics at both east- and west-flowing glacier margins.
Motivations for continued operation of the sensor network until 2020
Sustaining maintenance of and data collection from the existing sensor network will continue the flow of
near-real time data on meteorology, ice dynamics, and crustal motion. This, in turn, is necessary to make
possible existing and new research into rapid glacier and climate change by not only the PIs of this
proposal but a wide range of both collaborators and other researchers within the US and internationally.
In addition, the LARISSA sensor network has now become the core of a geographically larger network
supported by other national Antarctic research programs, for example an Australian Research Council
award to one of our collaborators (Matt King, U. of Tasmania) to extend observations of crustal motion
(via cGPS) to the south, in the hinterlands of the Larsen C ice shelf system. Although we can not
anticipate all the avenues of research that the broader community may conduct using the LARISSA
sensor network data, here we highlght some specific outcomes that the PIs of the present proposal aim to
achieve during the proposal period.
Visco-elastic response of earth’s crust. Our original goal for the LARISSA network was to better constrain
isostatic rebound in the Larsen embayment that reflected unloading following the Last Glacial Maximum.
However, observed rates of crustal motion were much greater than expected, which led to the
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conclusions that (i) a significant portion of observed crustal motion reflected recent collapse of the Larsen
B ice shelf, and (ii) by implication, the mantle viscosity beneath the AP is unusually low (Nield et al.,
2014). As the remaining ice shelves in the Larsen system continue to change (i.e., Paolo et al., 2015;
Khazendar et al., 2015), we argue that it is critically important to maintain our observations of crustal
motion in order to better quantify and understand viscoelastic rebound associated with glacier change in
this region. This is a unique natural experiment that can continue to pay large scientific dividends in the
glaciologic and geodetic communities, but only if we can maintain the viability and functionality of the
sensor network.
Table 1. Instrument stations to be managed in this proposal (see Figure 1 for locations).
Location
Duthier’s Pt.*
Site
Name
Type
Lat.°S
Lon.°W
Elev
(m)
Install
date
Need
DUPT
cGPS-Met
64.805
62.817
43
Apr-09
Retrieve seismic data
Hugo
HUGO
cGPS-Met
64.963
65.668
20
Apr-09
Refurbish/replace Met pack
Vernadsky
VNAD
cGPS-Met
65.246
64.254
19
Apr-09
No need at present
Robertson Is.
ROBN
cGPS-Met
65.246
59.445
56
Jan-10
New flash memory
Cp. Framnes
CAPF
cGPS-Met
66.012
60.558
100
Feb-10
Foyn Point*
FONP
cGPS-Met
65.245
61.646
87
Feb-10
Spring Pt.*
SGPT
cGPS-Met
64.295
61.052
55
May-13
New flash memory
New flash memory, retrieve
seismic data
New flash memory
Prospect Pt.*
PRPT
cGPS-Met
66.007
65.339
20
Apr-14
Flask Gl. (u)
FLSK
iceGPS-M
65.752
62.897
550
Feb-10
Leppard Gl.
LPRD
iceGPS-M
65.953
62.904
594
Feb-10
Flask Gl. (l)
FASK
AMIGOS
65.777
62.686
406
Feb-10
Scar Inlet
SCAR
AMIGOS
65.780
61.936
40
Feb-10
Cp. Disappt.
CDPT
AMIGOS
65.561
61.751
234
Nov-11
Replace 2 batteries
Reset solar panels, new flash
memory
Reset solar panels, new flash
memory
Replace CPU encl., reset solar
pnls, bat.
Optional: reset station on stable
ice
Retrieve data
Notes: (u) = upper, (l) = lower section of glacier.
* stations with passive seismic recorders for detecting glacier calvings and other events.
Positions are latest available locations for moving stations.
cGPS: continuous GPS stations on rock outcrops for measurement of crustal motion.
iceGPS: continuous GPS stations on glaciers for measurement of ice motion changes..
AMIGOS: Automated Meteorology-Ice-Geophysics Observing System: camera, GPS, weather, firn thermistors, albedo
sensors.
For example, a mantle velocity estimate for the nAP permits additional applications of GIA modeling that
the PIs (Domack and Scambos) and collaborators (Matt King, and others) will be pursuing (Domack et al.,
2015). Specifically, it is a significant advance that the isostatic response to recent loading provides a
mantle viscosity estimate that is independent of a specific LGM-to-present ice volume reconstruction. This
removes an important free parameter in relating observed isostatic rebound and relative sea level change
to the LGM-to-present ice loading history, and makes it potentially feasible to use RSL and rebound data
to unambiguously reconstruct LGM-to-present ice volume change. We will use this relationship to
evaluate new ice sheet reconstructions for the AP derived from geological data to (e.g., Lavoie, et al.,
2015; Golledge, 2014).
A better constrained LGM-to-present ice loading history then permits testing competing hypotheses for
external forcing of and internal feedbacks in LGM-to-present deglaciation of the region (Weber et al.,
2014; Golledge et al., 2014, 2015; Macintosh et al., 2011; Gomez, et al., 2013 ; Pollard et al, 2015 ).
Specifically, we note work that highlights the role of isostatic rebound on the stability of the grounding line
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of ice shelf ice stream systems during recession (Gomez et al., 2013). Rapid crustal response over small
spatial scales (the exact kind of behavior we have observed for the nAP) helps to stabilize ice margin
retreat in deep water and provides some restraint on the forcing factors that initiate ice sheet recession
from marine basins.
Figure 1. Map of northern Antarctic Peninsula combining recent DEM of the Peninsula (Cook et al, 2013) and
bathymetry from compiled sonar measurements (Lavoie et al., 2015), showing locations of the 14 sites having
sensors installed. UNAVCO PoleNet-style cGPS and iceGPS units are shown as blue hexagons; AMIGOS units
are shown as maroon hexagons (an earlier AMIGOS station at the Bruce Plateau ice core site is now buried and
inaccessible).
Glacier basin-scale mass balance changes from localized uplift . Another potential application of the cGPS
results is the resolution of spatial variation in localized glacier surface mass balance across the nAP.
Currently the nAP shows an asymmetric response to changing climate and wind patterns. The dominance
of westerly winds associated with increased SAM indices has lead to pronounced warming on both sides
of the AP. Yet this is expressed by dramatic increases in accumulation on the windward (western) side of
the AP (Fig. 2) and increased ablation and surface melting on the leeward (eastern) side of the AP. Both
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sides have warmed as a result of the wind changes, but for very different reasons: in the west, the
warming is related to reduced sea ice and airflow from the northwest over open ocean; in the east,
amplified warming, melting, and ablation occurs as a result of downsloping foehn winds (Cape et al.,
2015).
The increase in accumulation over the past 60 years, and the recent high values (i.e. ~3 m w.e. at Site
Beta as observed for the 2010 season), have allowed western side glaciers of the nAP fjords to maintain
calving line positions, or to retreat very slowly (Ferrigno et al., 2008; Cook et al., 2005), and in general
have made them resistant to the impacts of strong summer melt seasons by the thickness of the firn pack
and retention of cold winter temperatures at depth (i.e., Pettit et al., 2014). The effect of warm dry air,
related to foehn winds on the eastern side, has not only contributed to the collapse of the Larsen B Ice
Shelf through surface melting (Scambos et al., 2003; Shuman et al., 2011; Scambos et al., 2014; Cape et
al., 2015) but has also contributed to the lowering of surface elevations for the major glaciers in the
eastern nAP through reduced net accumulation. Lowering of glacier surfaces and increased ablation has
isolated former tributary glaciers and decreased their accumulation zones. This shift of the mean
accumulation of snow mass can, potentially, be observed in our cGPS data when it is combined with
meteorological data from the sensor network and satellite stereo images and/or satellite altimetry from
other sources.
Figure 2: Top panel, record of annual accumulation (in meters of water equivalent) for the 810 years prior to 2010
as recorded in the Site Beta Ice core on Bruce Plateau (see Fig. 1). Data are averaged in 11 year bins. Provided
courtesy of Ellen Mosley-Thompson (personal communication, March, 2015). Note pronounced multi decadal and
centennial trend as well as the persistent increase in accumulation since ~1960. This trend correlates strongly with
borehole temperature-derived mean surface temperature history for the period 1810 - 2006 (blue outline in top
panel), using data from the AMIGOS Site Beta thermistor string and thermistor profile, bottom panel (Zagorodnov
et al., 2012).
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We believe that initial results of modeling the regional rebound resulting from the post-Larsen B breakup
surge in glacier outflow, and removal of a residual background signal from our network from a far field
station ( e.g., HUGO) show this effect (Fig. 3). For example, Robinson Island (ROBN) shows significantamplitude seasonal mass gain and loss, which may reflect seasonal changes in snow and ice loading.
Stations on the western side show smaller-amplitude seasonal changes (Fig. 3). However, discontinuous
operation of CAPF and FOYN makes it difficult to evaluate this; station maintenance proposed here would
remedy this issue, thus permitting us to determine to what extent we can resolve seasonal variations inl
loading. Currently plans have been submitted to evaluate the flow velocity character of western side
glaciers and the physical oceanographic parameters that help regulate ice mass loss (see Current and
Pending for PI Domack). Maintenance of the LARISSA network would be critical to improving the
effectiveness of these complementary investigations, should they be supported.
Figure 3: Relative height anomalies for 8 cGPS stations of the LARISSA network (& PALM) modeled by removing
far field site of HUGO cGPS. Inter annual variations have variable resolution for each station at seasonal time
scales which we interpret to reflect annual shifts in mass during the ablation and accumulation cycle. Stations of
note to this proposal are SPGT (Spring Point) located at Cayley Glacier and PRPT (Prospect Point). These
stations were installed in 2013 and 2014, respectively. Data as processed by Matt King (personal communication,
2015).
Progression of Scar Inlet Ice Shelf toward break-up. In the aftermath of the disintegration of the Larsen B
Ice Shelf (e.g., Glasser and Scambos, 2008) the Scar Inlet remnant shelf has shown evidence of
significant structural weakening. Evolution of the shear margin on the northwest flank of the ice shelf has
shown a progression towards a narrow zone of complete rupture, and a concentration of shear (Scambos
et al., 2013a; Scambos et al., 2014b; Khazendar et al., 2015). Along the southeastern flank, a set of
major rifts have opened, in 2002 immediately after the disintegration (which have since become the ice
shelf front after calving a series of icebergs, in 2006 and 2008), again in 2003, and most recently in
September 2012, indicating increasing right-lateral shear on the southeastern side. The major feeder
glaciers of the remnant shelf, Flask and Leppard, have also shown significant acceleration (Scambos et
al., 2013a; Khazendar et al., 2015).
This is interpreted as resulting from the loss of backstress from the larger Larsen B ice shelf area, leading
to a significant change in the stress field of the remaining Scar Inlet ice. Reduced backstress from the
loss of the Larsen B appears to have resulted in an unstable Scar Inlet Ice Shelf, in which the current
stresses resulting from the influx of ice from the two major tributaries has increased beyond its capacity
for accommodation through deformation, and pushed it to a fracture response along the high shear-stress
areas. This is particularly evident along the northeastern shear margin in satellite images and in AMIGOS
image data overlooking the ice front.
This weakening has occurred without the advent of extensive surface melting or hydrofracture. Since
2006, there has been a general slight cooling trend in the regional nAP climate, and this is evident in the
AMIGOS and cGPS weather data (McGrath and Steffen, State of the Climate, Antarctica 2011; Fig. 4).
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Images from the AMIGOS stations and satellite data indicate few melt ponds on the surface in the 20102015 summer periods, although extensive surface snow and firn melting events have occurred. Instead,
rifting and calving on the ice shelf has increased dramatically, and ice shelf flow speed has increased.
Figure 4: Top, regional temperature trend from nAP long-term weather stations. Since 2000, and particularly since
2006, mean annual temperature in the nAP has been more variable, with a slight cooling trend (too brief to be
significant). Bottom, temperature record for all data from the AMIGOS stations installed in the Scar Inlet area, Feb.
2010 - March 2015. Despite record and near-record warm events (Feb 2013; March 2015) a slight overall cooling
trend for summer data is discernable.
Observations from the AMIGOS stations (which include a precision GPS) show that both Flask Glacier
and Scar Inlet have sped up since installation. In the case of Flask AMIGOS, which is sited approximately
8 km upstream of the grounding line, speed has increased more rapidly recently. Moreover the in situ
GPS data have detected short-term variations in speed potentially related to meltwater reaching the
glacier bed (Fig. 5).
Figure 5: Flask Glacier and Scar Inlet AMIGOS GPS data. Flask Glacier ice position has been detrended to show
the net position deviation from a mean ice flow speed of 0.72 m a-1. Short term speed increases, followed by
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slowing, are likely due to meltwater entering the sub-glacial system. Scar Inlet ice flow speed shows short-term
variations related to tidal cycles, and an overall increase through the period of record.
Figure 6: Overview of structural changes on the Scar Inlet Shelf. Left, satellite image pair from NSIDC’s AGDC
data center for the six-year period spanning the LARISSA installation period, showing increased rifting and
extensive ice front fracturing, as well as development of the northwestern shear margin. North is up in the image,
note scale bar. Right, image series from the Cape Disappointment AMIGOS hi-res camera overlooking the Scar
Inlet Ice Shelf front and calving progression. The timeseries provides a detailed insight into the mechanical effect of
pinning points on the ice shelf front, and the progression of grounded iceberg drift in the foreground. Image
panorama (not shown) spans the entire Scar Inlet front and adjacent sea ice.
At Scar Inlet, variations in ice speed with tidal cycles are superimposed on increasing ice flow speed from
2010 to 2013, but in recent years some slowing is observed, a result of some buttressing by the
persistent fast ice in the Larsen B embayment. This indication of sea ice influence on ice flow has been
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suspected, but not previously demonstrated as clearly as seen in the Scar Inlet GPS data set combined
with remote sensing data on sea ice extent.
To summarize, we argue that continued observation of the Scar Inlet / Flask Glacier / Leppard Glacier
system is a critical and possibly irreproducible opportunity to observe an Antarctic ice shelf-glacier system
as it evolves rapidly towards instability and ice shelf collapse. This is an extraordinary opportunity to
gather heretofore unavailable in-situ observations as the system undergoes a major break-up and
subsequent ice mass loss acceleration.
Figure 7: Temperature trends and surface erosion observed by the Larsen B embayment portion of the sensor
network during the warmest recorded air temperature event for Antarctica in March 23-24, 2015. Reported record
temperatures of 17.4°C and 17.5°C were recorded at Marambio and Esperanza Stations. The event was caused
by a prolonged föehn wind arising from a near-stationary high pressure area in the Drake Passage and a broad
area of low pressure at the base of the Peninsula. Bottom row of images, surface ablation and melt formation.
Surface ablation was ~28 cm. Temperature record provided by M. Cape (personal communication, April 2015).
Weather, climate, and Ice-atmosphere interactions. Beginning on March 23, 2015, and continuing for the
next 5 days, a major foehn event spanning the nAP warmed the region to record-breaking temperatures.
The highest temperature reached at a manned weather station at the northern tip of the Peninsula
(Esperanza) was 17.5°C, setting a new warmest-ever air temperature record for the continent. However,
LARISSA network recorded still-higher temperatures, reaching 18.7°C at the Foyn Point cGPS station
(Fig. 7). Cape Disappointment and Scar Inlet AMIGOS also recorded the event, and showed that the
higher stations (Foyn and Cape Disappt.) were affected earlier, and reached higher temperatures, than
the ice shelf site, providing insight into the synoptic meteorology of the event. Images at Scar Inlet
revealed significant ablation in the first day. A short study of the event using the LARISSA network and
reanalysis weather model records is already in draft form.
The event underscores the importance of föehn events on the climate of the nAP, but also demonstrates
that additional compounding factors are required for melt lake formation leading to hydrofracture of the ice
shelf. Because the event occurred in early autumn, the melt percolated into the snow and froze almost
immediately. Had the event occurred in summer, increased insolation would have potentially initiated a
feedback effect in which surface darkening due to melt and grain coarsening would in turn pre-condition
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the surface for further melting and snowpack warming. To summarize, this event shows the value of the
data produced by the network of 13 meteorology sensors on the LARISSA network in not only directly
quantifying weather, climate, and surface ablation forcing of ice shelf dynamices, but in supporting a
potential predictive capability for when warm conditions leading to break-out of the fast ice, and melt pond
formation, might occur.
Sample Collection For Cosmogenic-Nuclide Exposure Dating
The purpose of this part of the proposal is to leverage our proposed logistical plan to obtain geological
data needed to provide records of glacier and ice shelf change in the Larsen embayment that cover a
longer period than the last 20-30 years of satellite observation. Such records are needed to put recent
dramatic events in a longer-term perspective. Specifically, we aim to obtain data needed to i) gain
information about earlier ice shelf breakup events that are inferred from marine sedimentological
evidence to have taken place in the Holocene; ii) determine which ice shelves in the Larsen embayment
were subject to these past collapses, and iii) evaluate the hypothesis that periods of extremely rapid
deglaciation due to either successive collapse of ice shelves or episodes of rapid grounding line retreat
between topographically-controlled stable positions were a common feature of LGM-to-present
deglaciation at marine ice margins in Antarctica.
Figure 8. Cosmogenic-nuclide exposure-age data for the Larsen A embayment. Left panel, map of Larsen A
embayment showing sites at Sjogren Fjord and Drygalski Glacier (visited by Balco on NBP10-01) and at Cape
Marsh (visited by Dr. Yeong Bae Seong on Araon cruise of April-May 2013). Center, photograph of nunatak
(indicated by B on left panel) near north side of Drygalski Glacier. View is to the west and shows the calving margin
of the Drygalski Glacier. Numerous glacially transported erratics lie on ice-moulded bedrock at this site; we
collected and analysed the one shown in foreground of photo. Right panel, exposure-age data from sites at
Drygalski Glacier (red; from site noted "B" on left panel) and Sjogren Fjord (blue; from sites noted "A" on left panel).
We see two populations of erratics at low elevations: a set with middle Holocene exposure ages that presumably
record deglaciation from LGM conditions and ice shelf disappearance in the early Holocene; and a set with nearzero exposure ages that we hypothesize were emplaced by late Holocene regrowth of the Larsen A ice shelf. By
collecting additional erratic and bedrock from these and nearby sites we can potentially i) determine how many
Holocene ice shelf breakup and regrowth events took place, and ii) quantify the timing of these events and the
magnitude of associated ice thickness changes.
We propose to collect are cosmogenic-nuclide exposure ages from ice-free areas adjacent to major
glaciers that drain into the Larsen B embayment. This method has been widely used in Antarctica to
reconstruct past changes in ice thickness. Its premise is that glacially transported rock and sediment
quarried from glacier beds has not been exposed to the surface cosmic-ray flux, so contains a negligible
cosmogenic-nuclide inventory. Once deposited at a retreating ice margin, this material is exposed to the
cosmic-ray flux, so its cosmogenic-nuclide concentration is directly proportional to the deglaciation age of
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a site. In favorable circumstances, therefore, cosmogenic-nuclide exposure ages of glacially transported
clasts from a particular site display older exposure ages with increasing elevation, and the age-elevation
array records past glacier thinning at that location (e.g., Stone et al., 2003; Balco, 2011). As the majority
of existing information about past glacier change in the Antarctic Peninsula region is derived from
radiocarbon-dated marine sediment cores, complementing these data with terrestrial exposure-age data
is particularly important because i) exposure-age data from ice-free areas provide information about past
ice thickness in addition to past ice extent, information which cannot be directly obtained from marine
sedimentary evidence, and ii) exposure-age chronologies are completely independent of assumptions
about marine carbon reservoir effects and sedimentary recycling of carbon that are needed to interpret
radiocarbon ages from Antarctic marine sediments as true calendar ages, so permit testing of these
assumptions.
One aim of the LARISSA project was to collect samples for cosmogenic-nuclide exposure-dating from a
number of sites -- mostly ice-free areas adjacent to major glaciers -- on the east side of the Antarctic
Peninsula adjacent to existing and former parts of the Larsen Ice Shelf. However, weather and sea ice
conditions permitted visiting only a small fraction of our planned target areas. This included one area
adjacent to the former Prince Gustav Channel ice shelf (the Sjogren-Boydell glacier fjord; see Figure 8)
and one area adjacent to the former Larsen A ice shelf (the Drygalski Glacier grounding line area; see
Figure 8). Despite our very limited ability to collect samples, the exposure-age data that we did collect
made important contributions to our understanding of LGM-to-Holocene ice sheet and ice shelf change.
These results are summarized by Balco et al. (2013) and in part in Figure 8. First, we now have at least a
partial record of late-glacial and early Holocene ice thickness change in the region that, taken with
marine-geological data for contemporaneous changes in grounding line position, greatly improves our
ability to reconstruct LGM-to-present ice volume changes in the region. Second, exposure-age data from
both sites has the unusual property, which is unique to our knowledge among similar data in Antarctica,
that at low elevations glacially transported erratics with middle Holocene exposure ages co-occur with
erratics of similar appearance but extremely young exposure ages of only a few hundred years. As
discussed in Balco et al. (2013), we hypothesize that these two age populations record i) early-middle
Holocene deglaciation and complete ice shelf collapse, as well as ii) late Holocene ice shelf regrowth
prior to subsequent disintegration in recent decades. If true, this means that collecting similar data over a
wider north-south range can, with complementary marine-geological data (Rebesco et al., 2014; Domack
et al., 2005; Brachfeld et al., 2003), clearly show exactly which portions of the Larsen ice shelf system
were subject to Holocene collapse and regrowth. In addition, denser sample collection combined with the
method of “burial dating” with multiple cosmogenic nuclides with different decay constants can potentially
provide a chronology not only for glacier thinning during deglaciation events but also for glacier thickening
during ice shelf regrowth (e.g., Goehring et al., 2011).
In light of the extremely limited time available for geologic mapping and sample collection on the 2010
LARISSA cruise, we view the results of the exposure-dating research described above as an extremely
successful outcome. Our aim in the present proposal is to leverage our proposed plan for helicopter
access to instrument sites in the Larsen B embayment to carry out the exposure-dating research there
that was originally planned but could not be accomplished, and, potentially, also collect the increased
density of samples from the Larsen A area needed to develop an unambiguous chronology of Holocene
ice shelf collapse and regrowth. The ship and helicopter logistics needed to achieve these goals are fully
complementary to those required for upgrade and maintenance of the observing network,, and combining
these projects offers the potential for a significantly greater scientific payoff for the same investment in
logistical resources. Specifically, we propose the following efforts:
(1) Access to never-visited exposure-dating sites in the Larsen B embayment. In planning for the 2010
LARISSA cruise, we used satellite and high-elevation aerial imagery to identify a number of ice-free sites
adjacent to major glaciers that were likely to provide valuable exposure-age data. Subsequent overflights,
additional low-elevation aerial photography, and ground photography of the region during installation of
the existing observational network has allowed us to refine this list. Figures 9 and 10 highlight sites in the
vicinity of the Crane Glacier where helicopter access appears feasible and available evidence suggests
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that a glacial-geologic record of past ice thickness change exists. In addition, we have identified sites
adjacent to the Hektoria, Flask, and Leppard Glaciers that have similar characteristics.
(2) Access to previously visited and new sites in the Larsen A embayment. Here our objective is to collect
the higher density of samples of glacially transported erratics, as well as bedrock samples that were not
collected at all on the 2010 LARISSA cruise, that are needed to apply analysis of multiple cosmogenic
nuclides to potentially date both ice sheet/ice shelf thinning and thickening events.
To summarize, given several days of helicopter operations in the Larsen embayment, it is highly likely
that we can make significant progress towards both of these objectives. The proposed cruise would
present a rare and extraordinary opportunity to collect important samples. Our primary goal in this section
of the present proposal is that this opportunity not be missed.
Figure 9. Left panel, map of Larsen B embayment showing locations of ice-free areas where air photo
reconnaissance indicates that i) a helicopter landing is feasible, and ii) glacial deposits suitable for exposure-dating
are likely to be present. Right panel highlights sites adjacent to Crane Glacier. The image in the right panel, a 1969
U.S. Navy aerial photograph, shows the former Larsen B ice shelf prior to its 2002 breakup. The present glacier
front is shown by a dashed line. We (Scambos) made a helicopter landing in 2013 at the site nearest the present
ice front (highlighted in image); Figure 10 shows that site from the ground.
One additional note is that in this proposal we are only requesting funds necessary to put co-PI Balco and
a field team in the field to collect samples, and we are not requesting funds necessary for subsequent
cosmogenic-nuclide analysis. Based on past experience in this region and the complexity of access to the
sites, we view it as unrealistic to estimate in advance how many samples will be collected, and thus what
analytical funding is required. If we are successful in collecting samples, we will request analytical funds
commensurate to the actual sample set collected in a separate future proposal.
Logistical Support via U. S. Coast Guard Cutter Polar Star
Logistical planning for the original (2010) LARISSA cruise was predicated on a 10-year sea ice
climatology implying a high likelihood of open water access to the Larsen B embayment during the austral
summer. Thus, we assumed that the N.B. Palmer would be able to maneuver into close proximity to
target helicopter landing sites, and that the Bell 206L light helicopters aboard the Palmer would be
suitable for planned repeated short trips to sensor sites. However, this plan was not well suited to
unexpectedly severe summer sea ice conditions. Because the Palmer was not able to reach initially
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planned positions, helicopter access to the target sites required long flights and remote fuel caching, thus
greatly increasing disruption of operations by weather conditions and significantly reducing load capacity.
In fact, the on-ice AMIGOS had to be deployed via Twin Otter fixed wing support based from Rothera
Station. Since that time we have gained access to the region through the generous cooperation of the
Argentine Antarctic Division (2014) and significant support by the Korean Polar Research Institute
(KOPRI) via a cruise of the the RVIB Araon in 2013. In addition, cGPS stations on the western side of the
Peninsula have been periodically serviced and maintained by the USAP during occasional visits of the
L.M. Gould and the technical assistance of the shipboard ET and MT staff. However, this effort has been
ad hoc and opportunistic.
Figure 10. Site of helicopter landing adjacent to lower Crane Glacier in April 2013 (Figure 9, right panel above).
Note abundance of glacial erratics suitable for cosmogenic-nuclide exposure-dating across the outcrop surface.
.
We argue that the logistical plan outlined below represents the best strategy to obtain access to
the region under the significant uncertainty in sea ice regime and consequent uncertainty in the required
length and payload of helicopter flights. Specifically, we belive that the the USCGC Polar Star and its
complement of two HH-65 Dolphin helicopters best mitigates this uncertainty, for the following reasons:
1) The Polar Star has greater icebreaking capability than other icebreakers (ie. NPB Palmer, RVIB Araon,
Polarstern). This increases its ability to operate in difficult ice conditions that are likely in the
northwestern Weddell Sea. This increases the likelihood of a close approach to target sites, which in
turn decreases length, number of flights, and required payloads for helicopter flights as well as
reducing dependence on weather conditions.
2) The Dolphin helicopters have longer range and higher payload than other available options. This
permits achieving our objectives with fewer flights and without fuel caching from even non-optimal ship
poisitions, for example if the fast ice edge is significantly to the north or east of the target area as wase
the case in 2010. Higher payload and range also significantly reduces weather dependence by
reducing the required number of flights.
3) The Polar Star provides weather and flight operational capabilities not available on other USAP vessels
(L.M. Gould and N.B.P. Palmer).
4) The Polar Star is currently part of the USAP Antarctic logistical infrastructure, so has a dual science /
ice breaking mission. Shipboard science capabilities can easily accommodate our science needs.
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Potentially, it could be used to provide access to the Larsen B embayment either before or after the
McMurdo channel break in of January.
Field Plan, 2016-2017
We propose to utilize the Polar Star after the McMurdo break-in in the 2016-17 Antarctic field season.
This plan would involve a transit from McMurdo to Punta Arenas, Chile of about 17 days. Following this,
we request an on-site time of 14 days in the NW Weddell Sea with 3.5 days transit (each way). This
would put us in the Larsen region in early March, a period of usually good weather, suitable daylight
hours, and historically relatively open ice conditions. We estimate that we can accomplish all of our goals
of station upgrades and sample collection with 7 days of uninterrupted flight time, so our request woul
accommodate potential disruption of flight operations by weather. Although flight operations would be the
priority, during potential weather delays we propose that the Polar Star assist in location and recovery of
three oceanographic moorings which were deployed in the NW Weddell Sea in 2012 as part of LARISSA,
as well as contributing to bathymetric mapping of the inner continental shelf as feasible. After our cruise
the Polar Star would return to Punta Arenas, and then, presumably, to its home port of Seattle
.
We have been advised by UNAVCO that if we accomplish the maintenance of cGPS stations
proposed here, further maintenance will not likely be required, until our proposed extended removal date
of 2020. This reflects progress by UNAVCO on identifying and resolving the specific software and
hardware issues at our stations. Use of the Polar Star, as we propose herein, will also allow for the
formulation of a sound strategy to remove the entire network at some future date (i.e., 2020) by either
some combination of Twin Otter support out of Rothera, or one additional visit by a capable vessel
dictated by the evolving sea ice conditions and resource circumstance.
Annual Activities 2016-2020
PIs Domack and Scambos will annually meet with UNAVCO and periodically hold conference calls to
discuss the status of the sensor network. This team will provide semi-annual reports to the NSF and the
broader scientific community regarding needed service of the network stations and to highlight available
data and scientific outcomes of data analysis. Our objective is thus to improve and make more
transparent planning and engineering activities aimed at optimizing system function. A web site will be
established and maintained at USF-CMS which will feature science outcomes of the LARISSA network
and provide linkages with collaborating groups at UNAVCO, NSIDC, and POLENET.
Summary
Intellectual Merit: The existing data set from the Larsen B sensor network has delivered significant
scientific results. Continued operation will continue this record and has the potential to deliver truly
important, unique, and likely not otherwise obtainable data on ice sheet and ice shelf change in one of the
most dynamic parts of Antarctica.
Broader Impacts: The LARISSA sensor station array represents the kind of observation network that is
increasingly required to make further advances in understanding the impacts of climate and
oceanographic changes on the ice sheets and their trend towards increased mass imbalance. As an open
network generating publicly available data, continued operation of the network facilitates both scientific
study and public understanding of rapid ice sheet change across a broad range of audiences.
Results from Prior NSF Support
Citations in this section are listed in the reference section of the proposal, marked with *
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T. Scambos, E. Pettit, M. Truffer, E. Mosley-Thompson, and A. Gordon (B. Huber) Collaborative
Research in IPY: Abrupt Environmental Change in the Larsen Ice Shelf System – Cryosphere and
Oceans, OPP-732921, $$693,785, 05/01/08-04/30/14
Intellectual Merit: This project aimed to achieve an integrated understanding of ongoing and recent
changes in the ice, ocean, and biological systems of the northern Antarctic Peninsula (nAP). The project,
named LARISSA (Larsen Ice Shelf System, Antarctica), focused on sites of rapid climate and glacier
change in the nAP on both the east and west coasts. Heavy sea ice conditions on the eastern side led to
modifications in the research plan, but significant glaciological data were collected and several long-term
measurement stations were installed, most of which are still collecting data as described in this proposal.
Oceanographic data collected from the Larsen A region and in the western nAP fjords, combined with the
eastern-side sensor network is contributing to an understanding of the relative importance of ocean
versus atmospheric changes in causing the collapse of the Larsen A and B ice shelves and in
accumulation variations in the nAP.
Broader Impacts: A major article in Scientific American [Fox and Stenzel, 2012] discussed the LARISSA
project and Antarctic Peninsula climate change. LARISSA CryO contributed to undergraduate research
experiences (Anika Petach, U.Colo.; Emily Kreyerhagen, U.S. Naval Acad.; Jason Theis, U.Alaska) and
was the focus of 2 Ph.D. dissertations (M. Cape, Scripps Inst.; B. Goodwin, Ohio State Univ.). Further
development of the automated systems (AMIGOS) for ice observation was a major outcome of the work
and is leading to additional applications (including ongoing collaboration with Korean KOPRI scientists
and development of a climate-ice-ocean sensor station, AMIGOS-II).
Products: The LARISSA CryO group completed a site survey at the Bruce Plateau Site Beta site on the
nAP summit ridge in December 2009 [Pettit et al., in prep]. An ice core was drilled to bedrock (447m), and
a climate analysis of the past few centuries is near completion [Goodwin, 2014; Goodwin et al., 2015]. A
paleo-climate study based on borehole thermometry of the nAP Site Beta core [Zagorodnov et al., 2012]
reveals air temperature variations for the past ~130 years. A 3-D ice flow model of the nAP glaciers is
leading to both ice flux estimates into the fjords and the resultant delivery of nutrients to their ecosystem
[Pettit et al., in prep; Vernet and Pettit, 2015]. The team also conducted a radar, GPS, and remote
sensing survey of Röhss Gl. on James Ross Is. [Glasser et al., 2011]. We installed 4 multi-sensor
systems (Automated Met-Ice-Geophysics Systems, AMIGOS) [Scambos et al., 2013], 2 ice-sited cGPS
stations, and a passive seismic station. Ground-based radar surveys established glacier thicknesses
(Flask Gl. >1200 m; upper Leppard Gl. ~800 m; Röhss Gl. ~150 m). AMIGOS have documented
increasing flow speed and shear weakening of the Scar Inlet Ice Shelf. AMIGOS and GPS system
weather data have shown that föehn winds locally amplify regional warming and reduce the net
accumulation [Berthier et al., 2012; Cape et al., 2015; Scambos et al., 2014]. NBP1203 oceanographic
fieldwork included installation of 4 CTD/sediment trap moorings in the Larsen A embayment and
CTD/LADCP profiles in the Larsen A documenting continental shelf water masses, particularly modified
Weddell Deep Water, a derivative of Circumpolar Deep Water that has potential temperatures of a few
tenths °C. Increased winds in the region as Antarctic westerlies have intensified have resulted in reduced
sea ice in the northwestern Weddell in the 1990s and early 2000s. This appears to have led to some
increased basal melting of the Larsen A and B shelf ice, triggering a weakening of the shelf and
susceptibility to melt-driven hydrofracture [Scambos et al., 2014b]. Glaciological data from LARISSA CryO
will be stored at NSIDC / AGDC in early 2016.
Domack et al.; Collaborative Research in IPY: Abrupt Environmental Change in the Larsen Ice Shelf
System, a Multidisciplinary Approach-Marine and Quaternary Geosciences (LARISSA) OPP-ANT
0732467, $567,000; 10/2007-09/2014. Balco was a non-PI participant in this project.
Intellectual Merit: Two major research cruises to the Antarctic Peninsula, NW Weddell Sea were
conducted under USAP support during this award. In addition a small scale cruise and an international
expedition (aboard the KOPRI ship RVIB Araon) were also conducted. Results to date include papers
published in: Proceedings Royal Society-B (Smith et al., 2011), Deep Sea Research-II (Gutt et al., 2010),
Radiocarbon (Rosenheim et al., 2013), Science (Rebesco, Domack et al., 2014), Earth & Planet. Science
Reviews (Nield, et al.., 2014), Geol. Society America Bulletin (Christ et al., 2015), and The Cryosphere
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(Lavoie, Domack, et al., 2015). Our results have clarified the role of surface meteorological processes on
the collapse of the Larsen Ice Shelf, have refined radiocarbon dating methods in glacial marine and
lacustrine sediments, and have expanded biological studies in fjord regions on both sides of the
Peninsula. Further work on crustal rebound has helped constrain mantle viscosities in the region and
resolved the use of cGPS data as a mass balance indicator for Antarctic Peninsula glaciers. The work of
Dr. Greg Balco (Berkeley Geochronology Center) was also directly supported by this award and his
studies resulted in a paper in Quaternary Science Reviews (Balco et al., 2013).
Broader Impacts: A short course was successfully held for international undergraduate students in 2010
where the science and logistics of the LARISSA project was the focal point of the educational experience.
Eight undergraduate student theses were completed as part of this project and two major papers were
written for the science community by participating science journalist Douglas Fox (Scientific American,
2012 and Nature, 2013). Outreach activities were conducted to local classrooms at all grade levels by the
participating scientists. LARISSA web site and cruise blogs were posted to Hamilton College are
maintained by that institution (see: http://www.hamilton.edu/expeditions/larissa).
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