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Wendy Ermold

Physicist IV





Department Affiliation

Polar Science Center


Seasonality of Circumpolar Tundra: Ocean and Atmosphere Controls and Effects on Energy and Carbon Budgets

Through this project, investigators will characterize the seasonal linkages between the land surface greenness and a suite of land, atmosphere, and ocean characteristics, focusing on the Beringia/ Beaufort Sea, where there have been strong positive increases in the Normalized Difference Vegetation Index (NDVI) over the past 25 years, and the west-central Arctic Eurasia region, where the NDVI trends have been slightly negative. This is a collaborative project led by Howard Epstein at the University of Virginia with Uma Bhatt, Univ. of Alaska, Fairbanks, and Mike Steele, University of Washington.



Polar Science Weekend @ Pacific Science Center

This annual event at the Pacific Science Center shares polar science with thousands of visitors. APL-UW researchers inspire appreciation and interest in polar science through dozens of live demonstrations and hands-on activities.

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10 Mar 2017

Polar research and technology were presented to thousands of visitors by APL-UW staff during the Polar Science Weekend at Seattle's Pacific Science Center. The goal of is to inspire an appreciation and interest in science through one-on-one, face-to-face interactions between visitors and scientists. Guided by their 'polar passports', over 10,000 visitors learned about the Greenland ice sheet, the diving behavior of narwhals, the difference between sea ice and freshwater ice, how Seagliders work, and much more as they visited dozens of live demonstrations and activities.

The Polar Science Weekend has grown from an annual outreach event to an educational research project funded by NASA, and has become a model for similar activities hosted by the Pacific Science Center. A new program trains scientists and volunteers how to interact with the public and how to design engaging exhibits.

Arctic Switchyard

Like a railroad switchyard where loads come together, rearrange, and exit, the water masses of the Arctic Ocean are tracked as they move toward the North Atlantic Ocean.

1 Nov 2010


2000-present and while at APL-UW

Changing seasonality of panarctic tundra vegetation in relationship to climatic variables

Bhatt, U.S., D.A. Walker, M.I. Raynolds, P.A. Bieniek, H.E. Epstein, J.C. Comiso, J.E. Pinzon, C.J. Tucker, M. Steele, W. Ermold, and J. Zhang, "Changing seasonality of panarctic tundra vegetation in relationship to climatic variables," Environ. Res. Lett., 12, doi:10.1088/1748-9326/aa6b0b, 2017.

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5 May 2017

Potential climate drivers of Arctic tundra vegetation productivity are investigated to understand recent greening and browning trends documented by maximum normalized difference vegetation index (NDVI) (MaxNDVI) and time-integrated NDVI (TI-NDVI) for 1982–2015. Over this period, summer sea ice has continued to decline while oceanic heat content has increased. The increases in summer warmth index (SWI) and NDVI have not been uniform over the satellite record. SWI increased from 1982 to the mid-1990s and remained relatively flat from 1998 onwards until a recent upturn. While MaxNDVI displays positive trends from 1982–2015, TI-NDVI increased from 1982 until 2001 and has declined since. The data for the first and second halves of the record were analyzed and compared spatially for changing trends with a focus on the growing season. Negative trends for MaxNDVI and TI-NDVI were more common during 1999–2015 compared to 1982–1998.

Trend analysis within the growing season reveals that sea ice decline was larger in spring for the 1982–1998 period compared to 1999–2015, while fall sea ice decline was larger in the later period. Land surface temperature trends for the 1982–1998 growing season are positive and for 1999–2015 are positive in May–June but weakly negative in July–August. Spring biweekly NDVI trends are positive and significant for 1982–1998, consistent with increasing open water and increased available warmth in spring. MaxNDVI trends for 1999–2015 display significant negative trends in May and the first half of June.

Numerous possible drivers of early growing season NDVI decline coincident with warming temperatures are discussed, including increased standing water, delayed spring snow-melt, winter thaw events, and early snow melt followed by freezing temperatures. Further research is needed to robustly identify drivers of the spring NDVI decline.

Loitering of the retreating sea ice edge in the Arctic Seas

Steele, M., and W. Ermold, "Loitering of the retreating sea ice edge in the Arctic Seas," J. Geophys. Res., 120, 7699-7721, doi:10.1002/2015JC011182, 2015.

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1 Dec 2015

Each year, the arctic sea ice edge retreats from its winter maximum extent through the Seasonal Ice Zone (SIZ) to its summer minimum extent. On some days, this retreat happens at a rapid pace, while on other days, parts of the pan-arctic ice edge hardly move for periods of days up to 1.5 weeks. We term this stationary behavior "ice edge loitering," and identify areas that are more prone to loitering than others. Generally, about 20–25% of the SIZ area experiences loitering, most often only one time at any one location during the retreat season, but sometimes two or more times. The main mechanism controlling loitering is an interaction between surface winds and warm sea surface temperatures in areas from which the ice has already retreated. When retreat happens early enough to allow atmospheric warming of this open water, winds that force ice floes into this water cause melting. Thus, while individual ice floes are moving, the ice edge as a whole appears to loiter. The time scale of loitering is then naturally tied to the synoptic time scale of wind forcing. Perhaps surprisingly, the area of loitering in the arctic seas has not changed over the past 25 years, even as the SIZ area has grown. This is because rapid ice retreat happens most commonly late in the summer, when atmospheric warming of open water is weak. We speculate that loitering may have profound effects on both physical and biological conditions at the ice edge during the retreat season.

Modeling the formation and fate of the near-surface temperature maximum in the Canadian Basin of the Arctic Ocean

Steele, M., W. Ermold, and J. Zhang, "Modeling the formation and fate of the near-surface temperature maximum in the Canadian Basin of the Arctic Ocean," J. Geophys. Res., 116, doi:10.1029/2010JC006803, 2011.

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12 Nov 2011

A numerical model is used to investigate the time and space extent of the near-surface temperature maximum (NSTM) of the Canadian Basin of the Arctic Ocean over the years 2000%u20132009. The NSTM is formed from local summertime absorption of solar radiation which, in some circumstances, descends through the fall and early winter to form a warm subsurface layer just below the winter mixed layer. We find that winter survival of this layer is confined largely to the Beaufort Gyre of the Canadian Basin, where Ekman convergence and downwelling push the summer warm layer down below the winter mixing depth. In recent years, summer stratification has increased, downwelling has accelerated, and the NSTM has warmed as the sea ice cover in the Beaufort Gyre has thinned. The result is a strengthening NSTM which contained enough heat by the end of winter 2007/2008 to melt about 20 cm of sea ice. Northwest of Alaska the model also simulates a second, deeper temperature maximum layer that forms from advection of saltier summer Pacific water. However, this layer is difficult to adequately resolve and maintain given the model's resolution.

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Mechanisms of summertime upper Arctic Ocean warming and the effect on sea ice melt

Steele, M., J. Zhang, and W. Ermold, "Mechanisms of summertime upper Arctic Ocean warming and the effect on sea ice melt," J. Geophys. Res., 115, doi:10.1029/2009JC005849, 2010.

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6 Nov 2010

In this study, we use a numerical sea-ice-ocean model to examine what causes summertime upper ocean warming and sea ice melt during the 21st century in the Arctic Ocean. Our first question is, "What causes the ocean to warm in the Pacific Sector during the summer"? We find that about 80% of total heating over this region comes from ocean surface heat flux, with the remaining 20% originating in ocean lateral heat flux convergence. The latter occurs mostly within a few hundred kilometers of the northwest Alaskan coast. In the summer of 2007, the ocean gained just over twice the amount of heat it did over the average of the previous 7 years. Our second question is, "What causes sea ice to melt in the Pacific Sector during summer"? Our analysis shows that top melt dominates total melt early in the summer, while bottom melt (and in particular, bottom melt due to ocean heat transport) dominates later in the summer as atmospheric heating declines. Bottom melt rates in summer 2007 were 34% higher relative to the previous 7 year average. The modeled partition of top versus bottom melt closely matches observed melt rates obtained by a drifting buoy. Bottom melting contributes about 2/3 of total volume melt but is geographically confined to the Marginal Ice Zone, while top melting contributes a lesser 1/3 of volume melt but occurs over a much broader area of the ice pack.

Narwhals document continued warming of southern Baffin Bay

Laidre, K.L., M.P. Heide-Jorgensen, W. Ermold, and M. Steele, "Narwhals document continued warming of southern Baffin Bay," J. Geophys. Res., 115, doi:10.1029/2009JC005820, 2010.

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23 Oct 2010

We report on wintertime data collected from Baffin Bay and northern Davis Strait, a major gateway linking the Arctic with the subpolar North Atlantic, using narwhals (Monodon monoceros) as an oceanographic sampling platform. Fourteen narwhals were instrumented with satellite-linked time-depth-temperature recorders between 2005 and 2007. Transmitters collected and transmitted water column temperature profiles from each dive between December and April, where >90% of maximum daily dive depths reached the bottom. Temperature measurements were combined with 15 helicopter-based conductivity-temperature-depth (CTD) casts taken in April 2007 across central Baffin Bay and compared with hydrographic climatology values used for the region in Arctic climate models. Winter temperature maxima for whale and CTD data were in good agreement, ranging between 4.0 deg C and 4.6 deg C in inshore and offshore Baffin Bay and in Davis Strait. The warm Irminger Water was identified between 57 deg W and 59 deg W (at 68 deg N) between 200 and 400 m depths. Whale data correlated well with climatological temperature maxima; however, they were on average 0.9 deg C warmer plus/minus 0.6 deg C (P < 0.001). Furthermore, climatology data overestimated the winter surface isothermal layer thickness by 50–80 m.

Our results suggest the previously documented warming in Baffin Bay has continued through 2007 and is associated with a warmer West Greenland Current in both of its constituent water masses. This research demonstrates the feasibility of using narwhals as ocean observation platforms in inaccessible Arctic areas where dense sea ice prevents regular oceanographic measurements and where innate site fidelity, affinity for winter pack ice, and multiple daily dives to >1700 m offer a useful opportunity to sample the area.

Tracing freshwater anomalies through the air-land-ocean system: A case study from the Mackenzie River Basin and the Beaufort Gyre

Rawlins, M.A., M. Steele, M.C. Serreze, C.J. Vorosmarty, W. Ermold, R.B. Lammers, K.C. McDonald, T.M. Pavelsky, A. Shilomanov, and J. Zhang, "Tracing freshwater anomalies through the air-land-ocean system: A case study from the Mackenzie River Basin and the Beaufort Gyre," Atmos. Oceans, 47, 79-97, doi:10.3137/OC301.2009, 2009.

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1 Mar 2009

Mackenzie River discharge was at a record low in water year (WY) 1995 (October 1994 to September 1995), was near average in WY 1996, and was at a record high in WY 1997. The record high discharge in WY 1997, with above average flow each month, was followed by a record high flow in May 1998, then a sharp decline. Through diagnosing these changing flows and their expression in the Beaufort Sea via synthesis of observations and model output, this study provides insight into the nature of the Arctic's freshwater system.

The low discharge in WY 1995 manifests negative anomalies in P–E and precipitation, recycled summer precipitation, and dry surface conditions immediately prior to the water year. The complex hydrograph for WY 1996 reflects a combination of spring soil moisture recharge, buffering by rising lake levels, positive P–E anomalies in summer, and a massive release of water held in storage by Bennett Dam. The record high discharge in WY 1997 manifests the dual effects of reduced buffering by lakes and positive P–E anomalies for most of the year. With reduced buffering, only modest P–E the following spring led to a record discharge in May 1998. As simulated with a coupled ice–ocean model, the record low discharge in WY 1995 contributed to a negative freshwater anomaly on the Mackenzie shelf lasting throughout the winter of 1995/96. High discharge from July–October 1996 contributed approximately 20% to a positive freshwater anomaly forming in the Beaufort Sea in the autumn of that year. The remainder was associated with reduced autumn/winter ice growth, strong ice melt the previous summer, and positive P–E anomalies over the ocean itself. Starting in autumn 1997 and throughout 1998, the upper ocean became more saline owing to sea ice growth.

Arctic Ocean surface warming trends over the past 100 years

Steele, M., W. Ermold, and J. Zhang, "Arctic Ocean surface warming trends over the past 100 years," Geophys. Res. Lett., 35, doi:10.1029/2007GL031651, 2008.

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29 Jan 2008

Ocean temperature profiles and satellite data have been analyzed for summertime sea surface temperature (SST) and upper ocean heat content variations over the past century, with a focus on the Arctic Ocean peripheral seas. We find that many areas cooled up to –0.5°C per decade during 1930–1965 as the Arctic Oscillation (AO) index generally fell, while these areas warmed during 1965–1995 as the AO index generally rose. Warming is particularly pronounced since 1995, and especially since 2000. Summer 2007 SST anomalies are up to 5°C. The increase in upper ocean summertime warming since 1965 is sufficient to reduce the following winter's ice growth by as much as 0.75 m. Alternatively, this heat may return to the atmosphere before any ice forms, representing a fall freeze-up delay of two weeks to two months. This returned heat might be carried by winds over terrestrial tundra ecosystems, contributing to the local heat budget.

Steric sea level change in the northern seas

Steele, M., and W. Ermold, "Steric sea level change in the northern seas," J. Clim., 20, 403-417, 2007.

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1 Feb 2007

Ocean temperature and salinity data over the period 1950%u20132000 in the Northern Seas, defined here as the North Atlantic Ocean (north of 50°N), North Pacific Ocean (north of 40°N), and Arctic Oceans, are combined to diagnose the steric (i.e., density) contribution to sea level variation. The individual contributions to steric height from temperature (thermosteric height) and salinity (halosteric height) are also analyzed. It is found that during 1950–2000, steric height rose over the study's domain, mostly as a result of halosteric increases (i.e., freshening). Over a shorter time period (late 1960s to early 1990s) during which climate indices changed dramatically, steric height gradients near the Nordic Seas minimum were reduced by 18%–32%. It is speculated that this may be associated with a local slowing of both the Meridional Overturning Circulation and the southward flow through Fram Strait. However, steric height increases in the North Pacific Ocean during this time imply a possible acceleration of flow through the poorly measured Canadian Arctic. Evidence that the Great Salinity Anomaly of the late 1960s and 1970s had two distinct Arctic Ocean sources is also found: a late 1960s export of sea ice, and a delayed but more sustained 1970s export of liquid (ocean) freshwater. A simple calculation indicates that these Arctic Ocean freshwater sources were not sufficient to create the 1970s freshening observed in the North Atlantic Ocean.

Salinity trends on the Siberian shelves

Steele, M., and W. Ermold, "Salinity trends on the Siberian shelves," Geophys. Res. Lett., 31, doi:10.1029/2004GL021302, 2004.

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24 Dec 2004

We present an analysis of observed long-term (~100 year) salinity trends on the freshwater-dominated Siberian continental shelves. A multiple regression was performed in the White Sea (WS), the Kara Sea (KS), the Laptev Sea (LS), and the East Siberian Sea (ESS). Since 1930, the WS has gained freshwater while the ESS has lost it, consistent with river discharge trends over this period. Over the past 20 years, increases in both river discharge and direct precipitation can explain observed salinity decreases in the WS, but not in the KS. Salinity trends in the LS and ESS indicate that ocean circulation plays a dominate role in these areas, where in recent years freshwater has been diverted eastward along the coast, rather than northward toward the deep ocean.

Circulation of summer Pacific halocline water in the Arctic Ocean

Steele, M., J. Morison, W. Ermold, M. Ortmeyer, and K. Shimada, "Circulation of summer Pacific halocline water in the Arctic Ocean," J. Geophys. Res., 109, C02027, doi:10.1029/2003JC002009, 2004.

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26 Feb 2004

We present an analysis of Arctic Ocean hydrographic and sea ice observations from the 1990s, with a focus on the circulation of water that originates in the North Pacific Ocean. Previous studies have shown the presence of two varieties of relatively warm "summer halocline water" in the vicinity of the Chukchi Sea, i.e., the relatively fresh Alaskan Coastal Water (ACW) and the relatively saltier summer Bering Sea Water (sBSW). Here we extend these studies by tracing the circulation of these waters downstream into the Arctic Ocean. We find that ACW is generally most evident in the southern Beaufort Gyre, while sBSW is strongest in the northern portion of the Beaufort Gyre and along the Transpolar Drift Stream. We find that this separation is most extreme during the early mid-1990s, when the Arctic Oscillation was at historically high index values. This leads us to speculate that the outflow to the North Atlantic Ocean (through the Canadian Archipelago and Fram Strait) may be similarly separated. As Arctic Oscillation index values fell during the later 1990s, ACW and sBSW began to overlap in their regions of influence. These changes are evident in the area north of Ellesmere Island, where the influence of sBSW is highly correlated, with a 3-year lag, with the Arctic Oscillation index. We also note the presence of winter Bering Sea Water (wBSW), which underlies the summer varieties. All together, this brings the number of distinct Pacific water types in our Arctic Ocean inventory to three: ACW, sBSW, and wBSW.

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