ABSTRACT:

This study analyzed the impact of climate variability on glaciers in the Olympic Mountains of Washington State, USA. The study area experiences a strong precipitation gradient, with annual precipitation ranging from 6.5 meters on the west-facing slopes to 0.5 meters in the northeast lowlands. We aimed to evaluate the hypothesis that the past asymmetry in glacier extent was driven by spatial variability in precipitation.

The data below is derived from the climate analysis of the 6-hour WRF model output taken during the OLYMPEX campaign from 2015-2016. "OLYMPICS_ELWHA_QUINAULT_6-HOUR_MEANS.csv" is the average precipitation within the Elwha and Quinault basins during each 6-hour model run in a csv format. "OLYMPEX_RAINNC_TOTAL.tif" is the sum of the RAINNC variable (representing total precipitation) throughout the entirety of the OLYMPEX campaign in a tif format.

ABSTRACT:

This MATLAB code models the flow of glaciers in the Elwha and Quinault basins of the Olympic mountains. The parameters used in the model, such as the density of ice, acceleration due to gravity, and parameters related to glacier deformation and sliding, are defined and set. The initial glacier profile is loaded from a file, either "Elwha_Basin_Input.mat" or "Quinault_Basin_Input.mat." The geometry of the glacier, such as its bed elevation and width, is defined and interpolated onto the model grid. Climate parameters, such as the annual precipitation, the temperature at sea level, and the melt factor, are also defined. The model then calculates the mass balance of the glacier, which is the difference between accumulation and melting. The height, thickness, and thickness rate of change of the glacier are modeled using a time loop, and the model outputs the height and thickness of the glacier over time.

ABSTRACT:

Glacier extent is known to be sensitive to climate variability through time. The impact of spatial variability in climate on glaciers has been much less studied. The Olympic Mountains of Washington State, USA, experience a pronounced precipitation gradient with modern annual precipitation ranging between ~6.5 meters on the high west-facing slopes to ~0.5 meters in the northeast lowlands. In the Quinault valley, on the west side of the range, a glacier extended onto the coastal plain reaching a maximum position during the early Wisconsin Episode glaciation. There is no evidence of a large Elwha glacier extending into the northeast lowlands at that time. We hypothesize that the asymmetry in past glacier extent was driven by spatial variability in precipitation. To evaluate this hypothesis, we first constrain the past precipitation gradient, and then model glacier extent. We explore variability in observed and modelled precipitation gradients over timescales from 6 hours to ~100 years. Across three data sets, basin-averaged precipitation in the Elwha is 54% of that in the Quinault, with variability of less than 15% at the annual timescale. Specifically, this ratio does not consistently vary with regional climate patterns. On average, modelled 6-hour accumulated precipitation in the Elwha is 78% of that in the Quinault during a winter season, with a few low-precipitation time periods exhibiting a flatter or even reversed precipitation gradient. Overall, our analysis does not suggest a mechanism for increasing the precipitation gradient, but overwhelmingly indicates spatially coherent variability in precipitation across the peninsula. We conclude that the past precipitation gradient was likely similar to the modern gradient. We use a one-dimensional glacier flowline model, driven by sea-level summer temperature and annual precipitation to approximate glacier extent in the Quinault and Elwha basins. We find several equilibrium states for the Quinault glacier at the mapped maximum position within paleoclimate constraints for cooling and drying, relative to today. We assume the Elwha remained drier than the Quinault, and model Elwha extent for the climates of the Quinault equilibria. At the warm end of the paleoclimate constraint (10.5˚C), the Elwha remains a small valley glacier in the high headwaters. Yet, for the cooler end of the allowable paleoclimate (7˚C), the Elwha glacier advances to a narrow notch in the valley. As the ice is forced to flow through a smaller cross-section, it thickens, triggering an ice-elevation feedback. This feedback leads to rapid extension of the Elwha glacier to elevations only ~100 meters above those reached by the Quinault. While there is uncertainty in the glacial record of the Elwha, it is unlikely that such a large glacier existed during the most recent glaciation. Therefore, we suggest that the last glacial maximum climate was more likely to have been within the warm end of the paleoclimate range. Alternatively, spatially variable drivers of ablation including differences in cloudiness could have contributed to asymmetry in glacier extent. Future research to constrain past precipitation gradients and evaluate their impact on glacier dynamics is needed to better interpret the climatic significance of past glaciation and to predict future response of glaciers to climate change.