Effect of a Warming North Pacific Ocean on LeConte Glacier · 2017-03-08 · Effect of a Warming North Pacific Ocean on LeConte Glacier Abstract The warming Pacific Ocean could affect

Effect of a Warming North Pacific Ocean on LeConte Glacier

Petersburg, AK. Photo credit: Helen Martin

By: Anders Christensen, Helen Martin, Joseph Giesbrecht, Henry Short, and Gabriel Torrez

Team: Higher Porpoise

Petersburg High School PO Box 289, Petersburg, AK 99833

contact person: Helen Martin at [email protected]

Coaches: Joni Johnson: [email protected]

Sunny Rice: [email protected]

“This paper was written as part of the Alaska Ocean Sciences Bowl high school competition. The conclusions in this report are solely those of the student authors.”

Effect of a Warming North Pacific Ocean on LeConte Glacier

Abstract

The warming Pacific Ocean could affect the mass balance of the LeConte Glacier, located near Petersburg, Alaska. In the North Pacific Ocean, sea surface temperatures have increased gradually, with a jump of 1-3˚ C since 2014. The Stikine Icefield is thinning at a −1.5 Gt yr-1 rate in marine terminating glaciers, a faster rate than that of land terminating glaciers. In this paper, we work to assess how ocean processes affect glacier mass balance. Subglacial discharge from LeConte Glacier meltwater lubricates the base of the glacier. Additionally, this cold meltwater creates upwelling which brings in warm ocean water and increases the rate of erosion at the glacier’s terminus, resulting in calving events. Currently, the LeConte Glacier is stable due to resting on the sill. If the sill erodes, LeConte would retreat 12 kilometers. Upwelling creates a rich and productive habitat within LeConte Bay. The bay harbors harbor seals, which rely on the glacier for protection from predators, source of food, and habitat. Little is known about how the changing glacier will impact harbor seals. Research is necessary to fully understand seal population biology as LeConte Glacier changes. This is important both biologically and economically. Tourism provides a steady income for several small fishing communities in Alaska. Moreover, seals are a large part of Native Alaskan culture and livelihood.

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Introduction

Standing on a boat roughly 100 meters from the LeConte Glacier, I realized two things--

that a rogue chunk of ice falling from the face could potentially cause a giant wave that could

easily overturn the boat, and that had I been standing in this same exact spot 30 years ago, I

would be frozen in ice. It was both a terrifying and humbling experience. The reason I was there

was because researchers have taken an interest in Petersburg Alaska’s nearby LeConte Glacier.

LeConte serves as an easily accessed model for Greenland’s glaciers that are likely to affect sea

level as they melt. Warming air temperatures impact glaciers, and scientists are looking at the

marine effects that a warming Pacific Ocean might have.

Sea surface temperatures (SST)

have been increasing since the turn of

the 20th century (EPA, 2016). In 1960,

the global SST was 0.11˚ C below the

1971-2000 average and since 1980 has

consistently been above that average

(Figure 1). In 2015, it was 0.1˚ C above

average. One recent local phenomenon

in the North Pacific Ocean, “The Blob,” deviates even more from the norm. This large mass of

warm water was noted beginning in 2014 and is typically 1-3˚ C warmer than normal. (Figure 2)

(NOAA NCDC, 2016).

Off the coast of Petersburg, our study community in southeastern Alaska, the temperature

has warmed by 2-3˚ C (NOAA NCDC, 2016). One hypothesized reason for this sudden warming

is that the Pacific Decadal Oscillation (PDO), has switched from a cold phase to a warming

Figure 1: The sea surface temperature anomalies from 1860 to 2014 (EPA, 2016).

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phase (Northwest Fisheries Science Center,

2016). Another reason for this increased

warming is a long-lasting El Nino pattern that

pushed warmed water from the western

Pacific to the eastern Pacific. The warmed

water then released a large amount of heat

that was trapped in the Western Pacific for

around a decade. This “Blob” was predicted

to disappear along with the El Nino in late

2015, but the North Pacific sea surface

temperature remains roughly 3˚ C above normal (Northwest Fisheries Science Center, 2016).

With an increase in temperature in the North Pacific, many different species and

environments will be affected. One of these environments will be the Stikine Icefield, which

feeds LeConte Glacier in

southeastern Alaska near

Petersburg (Figure 3). Named in

1887 after biologist Joseph

LeConte, the LeConte Glacier is

the Northern Hemisphere's

southernmost tidewater glacier

(Muir et al., 1917). In 1995

LeConte retreated by about 800

meters within five months. Three

Figure 2: Daily sea surface temperature anomalies showing the 1-3 ˚ C increase off the coast of southeastern Alaska (NOAA NCDC, 2014).

Figure 3: A map of Gulf of Alaska showing the LeConte Glacier and Petersburg (Gabriel Torrez Image).

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years later, in 1998 the glacier retreated 91 meters, making it one of the fastest retreating glaciers

at that time. However, since that time LeConte has stabilized (Melkonian et al., 2016). In this

paper, we will examine the effects of this warming water on the LeConte glacier and harbor seals

that depend on the glacier.

Terrestrial Effects On Glaciers

Glacier location, growth, and retreat are functions largely dependent upon snowfall and

rainfall. Glaciers are found typically in places of high snowfall and cold summers such as

southeast Alaska. The ratio of accumulation to ablation (mass loss from calving, evaporation, or

melting) during the summer is the determining factor of a glacier's growth (NSIDC, 2016). If

there is more mass lost from ablation than is gained through accumulation, the glacier will begin

to retreat. Globally, glaciers have tended to retreat in the past century primarily due to climate

change (UAF, 2013).

The Scenarios Network for Alaska & Arctic Planning (SNAP) shows that we are already

experiencing an increase in temperature. SNAP also projects that in the next few decades

freezing temperatures will become less frequent in southeast Alaska. Although precipitation is

projected to increase, combined with rising temperatures, precipitation in the form of snow will

decrease (Figures 4 and 5) (UAF, 2013).

Figure 4: Average Month Temperature for Juneau, Alaska (UAF, 2013).

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The result has been a decrease in mass at the Stikine Icefield at a rate of −3.3 ± 1.1 Gt yr-1

between 2000 and 2013/2014 (Melkonian et al., 2016). This mass loss is caused by a

combination of thinning and retreat; however, we do not understand how much each factor

contributes to total mass loss. Melkonian also found that marine terminating glaciers in the

Stikine Icefield such as LeConte are thinning at a rate of −1.5 ± 0.3 Gt yr-1 which is faster than

the land terminating rate of −0.9 ± 0.4 Gt yr-1 (Melkonian et al., 2016). This result suggests that

the ocean plays a significant role in the mass loss of Stikine Icefield and by extension, the

LeConte Glacier.

Marine effects on glaciers

In 1998, LeConte Glacier receded 91 meters. After this retreat the glacier stabilized

where it is today and has not advanced nor retreated significantly. If the glacier were to become

unstable from this point it is believed that LeConte will retreat 12 kilometers before stabilizing

again (Trautman, pers comm, 2016). Even though LeConte has stabilized it has been thinning

(Table 1). These changes in LeConte are impacted by complex ocean processes such as

subglacial discharge, ice shelf, and sills.

Figure 5: Average monthly precipitation for Juneau, Alaska (UAF, 2013).

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Subglacial Discharge

Subglacial discharge affects the glacier by eroding away the face of the terminus. The

surface of the glacier is exposed to heat energy from the sun, which melts the ice on top of the

glacier. The melted water works its way through crevices and into a subglacial channel running

through and lubricating the glacier. The freshwater in the channel is put under immense pressure

by the glacier and allows the freshwater to be

super-chilled. At the terminus, the water jets

into the fjord. Being less dense than the

saltwater it rises, mixing with the warmer

saltwater. This action cuts away at the

terminus, increasing the mixing rate, which

pulls the warmer saltwater towards the

terminus face due to the forced convection of

the fresh water interacting with saltwater. This

creates a positive feedback loop where the

melting rate is increased by the discharge rate

(Jonathan Nash, pers comm, 2016).

Ice Shelf effects on melt rate

An ice shelf is a large piece of ice hanging off of the terminus of the glacier. The

subglacial discharge exaggerates ice shelf formation by eroding the terminus. Ice shelves are

affected by the tide as well. The rise and fall of the tide stresses the ice, increasing the calving

rate. Tidal mixing cuts into the ice shelf, weakening the shelf and increasing the calving rate as

well (Jonathan Nash, pers comm, 2016).

Table 1: LeConte Glacier depth of ice at the terminus. Data summarized from O’Neel, 2003; Motyka, 2003; Trautman, pers. comm., 2016

1998-2003 2015

Ice cliff height above water line (meters)

40-60 39-42

Ice below water line (meters)

200 200

Terminus above Flotation (meters)

25 -

Angle of Terminus Face

8°-12° 8°-12°

Flow rate of glacier (meters per day)

25

25

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Sill’s effect on glaciers

Moraines or sills are made by sediment that is carried down by the glacier. The sill holds

back the glacier when it is in contact with the terminus, preventing it from advancing. Tidal

mixing cuts away the terminus in contact with the sill. Once enough of the terminus erodes off,

the glacier will either advance back onto the sill or the subglacial discharge will erode the sill

away. Eventually, the sill is eroded away and the glacier starts an unstable advance. During this

event, the calving rate increases. This cycle continues until the glacier reaches another sill and

gets caught on it, restarting the process (Jonathan Nash, pers comm, 2016).

This is important to understand because the subglacial discharge affects the mass balance

of the glacier as well. Loss of ice due to calving at the terminus in Greenland was 56% total mass

loss (Reeh, 1994), and 77% in the Antarctic ice sheet (Jacobs et al., 1992; Reeh, 1994). A study

by Motyka (2003) shows that the submarine melt contribution to its loss at the terminus of

tidewater glaciers is driven by “forced convection at the ice–water interface driven by subglacial

discharge of fresh water and the influx of warm saline water.”

LeConte Sill

When the glacier retreats, the sill left behind acts as a reef. In some glacial systems, this

reef controls the mixing rate in the fjordal system and controls the flow rate in and out of the

fjord. The depth of water above the sill outside of LeConte Bay is between two and nine meters.

Due to forced convection, the fresh water leaves the bay while the saltwater enters. This

regulates the temperature inside of the bay. The salt water enters on the incoming tide, while

outgoing tide brings the fresh water out. During increased rainfall or melt rate, freshwater can

leave on outgoing tides (Jonathan Nash, pers comm, 2016).

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If the water temperature in Frederick Sound were to rise, this action at the sill would

allow warmer water into LeConte Bay. With warmer water in the LeConte Bay, the mixing rate

at the terminus would increase and be more impactful. This would erode the terminus faster,

allowing for an event where the terminus is able to overcome the sill, allowing for the retreat of

the glacier. Even though there is a depth of knowledge on the mechanics of tidewater glaciers,

there is little known about how this affects the food web in LeConte Bay.

Productivity within tidewater glaciers

Where glaciers reach the sea they form productive marine habitats. Through glacial melt

and surface rainfall that traverse through channels within the glacier, glacial water interacts with

the subglacial bed, influencing erosion rates (O'Neel, 2010). The water released into fjords

increases circulation within the fjords, ice melt below the water surface, and marine productivity

(Bartholomaus et al., 2015). The timing and magnitude of water flow also affects the biological

productivity.

Organic nutrients from the glaciers significantly affect productivity in glacial-marine

pelagic food webs (USGS, 2016). The microbial communities supported by the glacier affect the

cycling and release of nutrients and organic matter (O’Neel et al., 2015). Organisms around the

glacier, such as phytoplankton, rely on the glacial meltwater runoff and ocean mixing for

sustenance. In a process where freshwater and meltwater are mixed, nutrients from deeper fjord

waters are drawn into the photic zone, and high phytoplankton productivity is seen at the glacier

front. These upwelling events provide nutrient-rich water in the spring and late summer/early

fall, stimulating the primary production in the fjord, particularly at the glacier terminus (Juul-

Pedersen et al., 2015). Plankton is a staple of the glacial food web, as the nutrients contained

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provide food for many organisms. Glacial food webs include plankton, bottom-feeders, algae,

marine birds, and seals.

Foraging hotspots in tidewater glaciers form where large plumes of fresh water are

discharged from glaciers. Strong tidal mixing brings in ocean water and a high phytoplankton

biomass throughout the summer (Juul-Pedersen et al., 2015). The plankton become entrapped in

the freshwater plume rising to the surface and are stunned by this sudden change and often die

from the freshwater shock (Lydersen et al., 2013). The shocked plankton that survive become

easy prey at the surface of the water for surface feeders. Zooplankton can sometimes escape this

danger by moving below the rising water. However, in doing this they become concentrated in a

layer of water near the bottom, making them a plentiful and susceptible prey to benthic predators

(Lydersen et al., 2013).

In addition to the chemical and biotic factors, changes in the mass and volume of the

glacier can also impact these areas. Changes in the glacier size can alter the landscape, which in

turn alter habitats and processes within the glacier. As glaciers recede, living space and

conditions for organisms are altered significantly. The bay will become less saline with the

addition of freshwater, and algae that dwell within the glacier ice may be disrupted (O'Neel,

2010).

Seals

In LeConte Bay, Pacific harbor seals (Phoca vitulina) are the apex predator. Seals are

numerous in the secure bay and lounge on icebergs. Their diet consists of mollusks, crustaceans,

and numerous kinds of fish found in glacier bays. All of these organisms rely upon plankton in

the upwelling zone (Lundstrom et al., 2010). Females give birth to 25 pound (11 kg) pups while

on icebergs, nursing them for about a month. The pups nearly double in weight over this period

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of time. As the pups grow into adulthood, their weight will approach 180 to 280 pounds (81-127

kg) and they will eventually measure in at five or six feet in length (National Park Service, n.d).

Harbor seals found in glacial habitats generally had a better diet compared to their

terrestrial counterparts. Harbor seals are also free of predatory danger while on their haulouts,

and are able to reach them no matter if the tide is out or in unlike land-based haulouts (Blundell,

2009). Icebergs created by calving events on glaciers serve as a resting place and habitat for 10-

15% of all Alaskan harbor seals (NOAA, 2016). Surveying glacial ice is critical to correctly

estimating seal populations.

Population Trends

Tidewater glacier fjords in southeast Alaska

host some of the largest seasonal aggregations of harbor

seals in Alaska (Calambokidis, 1987). The only

information we have on harbor seal populations near

LeConte Bay is anecdotal: subsistence harvest survey

data indicates that Petersburg and Wrangell seal hunters

think that the population is increasing (Wolfe et al.,

2013). In the absence of hard data, we will use Glacier

Bay’s seals as Glacier Bay is home to several tidewater

glaciers. Two separate studies, one by the National Park

Service and one by the Alaska Department of Fish and

Game, have independently found that seals may be

changing their distribution and behavior to match the

shifting locations of ice as glaciers retreat. The National

Figure 6: Seal distribution is shown in the black dots in comparison to sea ice coverage (NPS, 2016).

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Park Service placed GPS trackers in seals to track their behavior to see how the change in the

glacier levels in Glacier Bay affect them. By 2008, no seals were pupping in Muir Inlet, and

fewer than 200 seals were counted in McBride Inlet, near the terminus of the McBride Glacier.

Both these locations were previously hotspots for seal activity but declined as the glacier

receded. Climate change models predict continual and rapid loss of glacial ice with unknown

impacts on organisms that rely on tidewater glaciers and tidewater glacial habitats (NPS, 2016).

Another example of seals following glacier ice is in John Hopkins Inlet, also part of

Glacier Bay. In Figure 6, aerial imaging shows that harbor seals congregate in areas of the Inlet

in red, with substantial ice coverage (NPS, 2016).

Seals routinely return to tidewater glacier fjords during pupping and molting seasons.

Glaciers provide icebergs into the marine environment due to calving, and these icebergs serve

as a habitat for harbor seals (Figure 6) (NPS, 2016). Although tidewater glaciers are naturally

dynamic, the advance and retreat of the glacier terminus due to climate change affects the habitat

of harbor seals. So far, the impacts at LeConte are unknown.

Effects & Economics

If LeConte Glacier begins to recede again, Motyka (2016) commented that the next

stopping point is 12 km up the bay, where the next sill is believed to be. When the sill is no

longer holding the glacier in place, the glacier will enter an unstable state. In this unstable state,

the glacier starts calving faster than it is flowing. This provides a greater habitat for harbor seals

until the glacier ceases to terminate in the bay. In this case, the glacier may stop calving which

will diminish habitat for harbor seals. Either way, this will cause tour ships to have to travel an

extra 12 km back to see the glacier, making it a greater time and fuel investment for tourists and

tour companies.

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According to Southeast Conference (2016), tourism in Southeast Alaska has been

growing and is projected to go up by 4% annually into 2020 (Southeast Conference, 2016).

Locally in Petersburg, LeConte glacier tours brought 624 people to the glacier and $162,986 in

earnings during 2009. These tours make up six percent of the total income from tourism in

Petersburg (Dugan et al., 2009).

In addition to the value for commercial and private sightseeing ventures, subsistence use

of seals in LeConte Bay should not be overlooked. Harbor seals are of cultural and spiritual

importance in Alaska Native communities. Alaska Fish and Game reports 15 harbor seals

harvested in 2012 in the Petersburg reporting area (Wolfe et al., 2013).

Management plan

According to NOAA’s complex integrated ecosystem assessment, “Successful resource

management depends on the ability to distinguish manageable human impacts from larger scale

climatic pressures. This necessitates long-term monitoring of physical and trophic responses to

climatic drivers as well as precautionary harvest and resource extraction strategies that provide

resiliency to stochastic climatic events” (NOAA, n.d). We have chosen to focus on the glacial

mass balance, interactions with the marine environment, and possible effects on harbor seals for

the formulation of a management plan.

We can do little to stop glacial mass balance changes, however, we can work to

understand the dynamic processes that affect the fjord, organisms, and people that use this

system. Petersburg High School students have annually been surveying the terminus position of

LeConte Glacier beginning in the 1980’s. More recently students have been measuring the height

of the glacier at the terminus. Currently, the researchers Jason Amundson, John Mickett, Roman

Motyka, Jonathan Nash, Eric Skyllingstad, and Dave Sutherland in the LeConte Bay system are

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gathering data on water properties, ocean circulation, near-glacier circulation, and the glacier

dynamics. They are also watching other changes in the glacier such as velocity, terminus

position, and thickness. Additional research could include using time lapse photography to track

retreat and a seismometer to register calving events.

As for the seal population in LeConte Bay, there needs to be more research done on the

population trends. Aerial digital imagery is a tool used to estimate the seal population and the

number of pups. Historically, counts were done manually, but now computers are being used.

Computers can tell the difference between icebergs, brash ice, water, and seals (Mitchell, 2016).

Another way we would need to monitor seals is by using GPS tracking to figure out where seals

could be moving to or going when not in LeConte Bay. We could also use drones to monitor the

seal population, such as with sea lions (Human, 2012). Lastly, ADFG needs to continue to

monitor the harvest of seals, including the amount of harbor seals being harvested and the effect

of people and boats on seals. The objective is to know the number of harbor seals harvested, their

age, and sex. If the harbor seal population falls past the prime sustainable population, then an

option would be to remove subsistence harvesting (NOAA, 2016).

Conclusion

In conclusion, we have examined how the warming Pacific affects tidewater glaciers,

specifically LeConte. Though LeConte is currently static, a warmer Pacific could prompt

LeConte to enter a retreat. The Stikine Ice Field is thinning and the tidewater glaciers are

thinning faster at .6 gigatons faster per year than the icefield. At ocean terminus subglacial

discharge increases lubrication of the glacier, and erodes the terminus. Stopping this retreat of

LeConte is the sill of the glacier; if the sill is eroded then LeConte could retreat around 12

kilometers. This change in glacial habitat will affect harbor seals, although exactly how at this

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time is unknown. More research needs to be done on seal populations and how the ocean

interacts with the glacier. Through these means, we would better understand the processes that

affect the LeConte Glacier and seals, both of which are culturally and economically important to

Petersburg.

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