Submarine melting of Greenland's glaciers: What are the
relevant ocean dynamics?
Submarine melting of Greenland's glaciers has emerged as a key term in
the ice sheets mass balance and as a plausible trigger for their recent
acceleration, which contributed to doubling Greenland's
contribution to sea-level rise. Notwithstanding its importance, understanding of submarine melting is
limited and it is presently absent or crudely parameterized in glacier,
ice sheet and climate models.
Greenland's tidewater glaciers end in ~600-800m deep, long fjords that
connect the margins of
the ice sheet to the shelf. The glaciers' termini are typically
grounded several hundreds of meters below
sea-level and, as such, are exposed to a thick portion of the fjords'
water column. Recently collected data from two large glacial fjords in south-east
Greenland (located in the Sermilik and Kangerdligssuaq fjords)
shows that these are filled year-round with cold, fresh waters of
Arctic origin and warm, salty waters of subtropical origin advected
into the fjords from the East Greenland Shelf (Straneo et. al., 2010,
Nature Geoscience, 3). This means that submarine melt rates may depend
on a suite of oceanic processes including externally forced fjord
circulations, fjord/shelf exchange and the distribution of properties
on the shelf. Yet,
the details of how these processes may contribute to the submarine melt
rate or affect its variability are
Fig.1. The study area with the location of the East
Greenland Shelf marked with a star
Schematic of the currents in the upper layer
superimposed on the modelled depth-averaged speed (m/s). Red (blue)
stands for warm (cold) currents. From Magaldi et. al., (2011), J. Phys.
Oceanogr., 41, p., 2308. The locations of the Sermilik and the
Kangerdlugssuaq Fjords are shown.
The project aims at identifying parameters and mechanisms which control
the properties and circulation in the south-east Greenland
fjords (see Fig.1-2) and thus the rate of submarine melting at the
We focus on two glacier fjords: Sermilik and Kangerdlugssuaq
(see Fig. 2). These two fjords have been in the focus of recent
observational campaigns (e.g., Straneo et. al., 2010, Nature
Geoscience, 3, Straneo et. al., 2011, Nature Geoscience, 4). The
observations suggest that the warm and salty Subtropical Atlantic Water
(STW) carried by the Irminger Current (IC) can flow onto the East
Greenland Shelf (EGS) and into the fjords (Fig.2). This warm water
inflow may significantly augment glacier melting in the fjords.
This work aims at investigating the inflow of the warm Atlantic-origin
water onto the shelf and into the mouths of the Sermilik and
The project has two phases.
First, we will use an existing configuration of a high resolution
regional ocean model with fields retrieved at at high sampling
rate and supplemented by Lagrangian particle simulations to study the
circulation on the East Greenland Shelf. By this, we aim at addressing
-- What are the pathways of Subtropical Atlantic Water (STW) on the
-- What processes control the inflow and variability of Subtropical
Atlantic Water (STW) onto the continental shelf?
-- What controls the property distributions at the fjord mouths?
Second, we will run the circulation model for a 20-year period to investigate
the interannual variability and to answer these questions:
-- How did environmental conditions before and after 1995 govern STW
intrusions onto the shelf?
-- How might future atmospheric and oceanic conditions govern STW
intrusions onto the shelf?
To perform these tasks, we employ a high resolution ocean model
validated by observations, and a Lagrangian particle code.
High resolution circulation model of the Irminger Basin
We use the MIT General Circulation Model (MITgcm) configured for the Irminger Basin area. The
-- Partial bottom cells and rescaled coordinate (for a better
representation of flows in a complex bathymetry)
-- Highest spatial resolution to date of the Irminger Basin: dx~2km,
dz=2-15m (210 layers), dt=30s
-- Simulation period: summer 2003 (7/1 - 9/1)
-- 3rd tracer advection with implicit diffusion; KPP for vertical
diffusion, Leith horizontal viscosity
-- Forcing by NCEP fluxes & SeaWinds
-- We verified that the model transports and hydrography agree with
For more details, see Koszalka, Haine, Magaldi (accepted to J. Phys.
Oceanogr.) who used this model configuration to study the dense water
The distribution of the Subtropical Atlantic Water in the model
First we looked into the distribution of the Subtropical Atlantic Water
(potential temperatures θ>=4 C) in the study area. The STW
constantly occupies the surface and sub-surface layers of the Irminger
Basin, with a prominent boundary flow of the Irminger Current along the
Iceland Shelf and along the East Greenland Shelf (Fig. 3a).
Occasionally, the STW flows onto the East Greenland Shelf and toward Sermilik Fjord (-38E, 65.5N) and Kangerdlugssuaq
Fjord (-31E, 68N). This inflow is steered by the bathymetric
depressions on the shelf: Sermilik Deep and Kangerdlugssuaq
Trough, respectively (Fig. 3b).
(a, left): Frequency of occurrence (in % of the 60-day
simulation period) of the Atlantic Subtropical Water (STW), defined as
waters of the potential temperature
higher than (θ=4 C). Superimposed are depth-averaged currents at the
depth range of 200-800m. (b, right): Bathymetry (depth of the sea bed)
in the study area.
We integrate the Lagrangian particles off-line with a code written
in MATLAB. At each time step, the simulated velocity fields (u,v,w
components) are linearly interpolated on current particle locations.
The particles are then advanced with MATLAB ode23t routine (2nd order
predictor, 3rd order corrector). The time step is 15 minutes, chosen
after a sensitivity study. For the boundary conditions, the code
identifies events of particles hitting the boundary (inevitable since
the time step for the Lagrangian code is larger than for the model
simulation) and resumes the time stepping with a particle put on the
boundary with the velocity component normal to the wall equal zero.
The code is available here: code download.
We performed two particle deployments in the STW layer: one at the
mouth of the Sermilik Fjord and one at the Kangerdlugssuaq Fjord.
The particle deployments are summarized in Table 1. Particles were
integrated backwards to study the pathways of the Atlantic Waters
to the fjords' mouths.
Table 1. Summary of the particle deployments at the mouth of the
Sermilik and Kangerdlugssuaq Fjords.
||Simulation length (days)
Trajectories of the Lagrangian particles
Trajectories of the backward-integrated particles deployed at the
mouths of the Sermilik and Kangerdlugssuaq Trough are shown in Fig.4.
The Animations of particles' positions are available here: MOVIES.
Trajectories of 38 backward-integrated Lagrangian
particles deployed at the mouth of the Sermilik Fjord (red)
and the 28 particles at the mouth of the Kangerdlugssuaq Fjord (dark
Note that the particles inflowing to the Sermilik Fjord (38 particles)
tend to follow the branch of the Irminger Current that separates from
boundary current flowing along the continental slope onto the shelf at
the Sermilik Deep. The particles arriving at the Kangerdlugssuaq Trough
(28 particles) come either from the branch of the Irminger Current
coming straight from the Irminger Basin or the
branch recirculating in the Denmark Strait. Two particles of this
latter set come from further north of the Denmark Strait with the dense
overflow water (see also Fig. 5 below). The Kangerdlugssuaq particles
reciculate in the Kangerdlugssuaq Trough before reaching
the fjord mounth.
Water property transformation
From the times series of water mass properties (temperature, salinity)
on particles we can identify the locations of the strongest
transformation, shown in Figure 5. The strongest transformation occurs
at the front between the Polar Waters and the Atlantic Waters
along the shelf break and in the Sermilik Deep.
For the particles released at the Sermilik Fjord, temperature-salinity (T-S) diagrams point to mixing between
the Subpolar Atlantic Water in the Irminger current, the Recirculating
Atlantic Water and the Polar Surface Water as the main process causing
the transformation. For the particles released at the Kangerdlugssuaq
Trough there is also evidence for mixing with the dense overflow (the
Arctic Atlantic Water mass).
Locations of strongest transformation (θ> 0.5C)
derived from one-day averaged time series of potential temperature
on the trajectories.
(a, left): T-S diagrams with marked potential
values for the particles released at the mouth of Sermilik Fjord
(blue dots) and the values
at the end of the simulation (brown crosses), linked by straight red
lines. (b,right): Same for the particles
released at the mouth of Kangerdlugssuaq Fjord. Abbreviations for
water masses (based on Rudels et. al., 2002, ICES J. of Mar. Sci., 59):
AW (Atlantic Water, or STW), RAW (Recirculating Atlantic Water), PSWw
(Polar Surface Water warm),
AAW (Arctic Atlantic Water).
-- The Atlantic Waters arrive at Sermilik Fjord through a
branch of the Irminger Current separating
from the boundary flow at Sermilik Deep.
-- The Atlantic Waters arrive at Kangerdlugssuaq Fjord with
either a branch of the Irminger Current coming directly from the
Irminger Basin or one recirculating in the Denmark Strait. Few
dense water overflow particles from the Denmark Strait are mixed into
this inflow as well.
-- The strongest transformation occurs at the frontal zone between
the Atlantic Waters and the Polar Surface Waters.
Inga Koszalka, Johns Hopkins University: firstname.lastname@example.org, http://blaustein.eps.jhu.edu/~koszalka/
Thomas Haine, Johns Hopkins University: Thomas.Haine@jhu.edu, http://www.jhu.edu/~thaine1/
This work is supported by NSF grant OCI-1129895. Particle simulations
have been performed on the Johns Hopkins Data-Scope funded by
Header photo: East Grenland, March 2007, by T. Haine