About

Dr. Patrick M. Alexander is an Associate Research Scientist in the Marine Geology and Geophysics division at the Lamont-Doherty Earth Observatory, Columbia Climate School. His research focuses on cryospheric science, specifically the interactions between ice and climate. He incorporates remote sensing, in situ measurements, and climate modeling to study ice-climate interactions, with particular emphasis on the interactions between climate and polar ice sheets. His goal is to understand the future impact of climate change on sea level rise. Dr. Alexander's background includes a Ph.D. in Earth and Environmental Science from the Graduate Center at CUNY, along with a master's and bachelor's degree in environmental engineering from Columbia University. His work involves assessing the variability and trends in Greenland's surface mass balance, ice sheet albedo, and the dynamics of glaciers and ice sheets, contributing to the broader understanding of climate change impacts on polar regions and sea level rise.

Research topics

• Climatology
• Environmental science
• Oceanography
• Geology
• Physical geography
• Geomorphology
• Geography

Selected publications

• Recent Variability in Fracture Characteristics and Ice Flow of Thwaites Ice Shelf, West Antarctica

  Journal of Geophysical Research Earth Surface · 2025-05-01 · 4 citations

  articleOpen access

  Abstract The rapidly changing Thwaites Ice Shelf is crucial for understanding ice‐shelf dynamical processes and their implications for sea‐level rise from Antarctica. Fractures, particularly their vertical structure, are key to ice‐shelf structural integrity but remain poorly measured. To address this, we developed a fracture‐characterization workflow using ICESat‐2 ATL03 geolocated photon heights, producing the first time‐series vertical measurements of fractures across Thwaites from 2018 to 2024. We introduced the fracture depth/freeboard ratio as a normalized metric to quantify vertical fracture extent, serving as an indicator of structural damage. This metric enabled us to track fracture evolution in both the eastern ice shelf and western glacier tongue. In the eastern section, fracturing intensified along the northwestern shear zone and near the grounding line, in a positive feedback loop between enhanced fracturing and accelerated flow. The western section maintained an active rift formation zone about 15 km downstream of the historical grounding line. Flow velocity changes in this section were primarily confined to the unconstrained downstream portion, exhibiting an overall deceleration trend, while the upstream area remained stable. This contrast highlights the role of lateral margin conditions in governing ice‐shelf fracture and flow behavior. Changes in the eastern section showed some correspondence with warm winter air temperatures, reduced sea ice, and persistent warm ocean anomalies at shallower depths, suggesting that atmosphere‐sea ice‐ocean interactions influence ice‐shelf structural integrity through basal processes. Future research should integrate satellite‐derived fracture observations with numerical models of ice fracture and flow to better capture the dynamics of ice‐shelf weakening and retreat.

  PublisherOA PDFDOI

• Dynamics of Future Soil Moisture Drought in Southwest North America: Linkages across Seasons in the Ocean–Atmosphere–Land System

  Journal of Climate · 2025-03-27 · 1 citations

  articleOpen access

  Abstract Southwest North America is projected by models to aridify, defined as declining summer soil moisture, under the influence of rising greenhouse gases. Here, we investigate the driving mechanisms of aridification that connect the oceans, atmosphere, and land surface across seasons. The analysis is based on atmosphere model simulations forced by imposed sea surface temperatures (SSTs). For the historical period, these are the observed ones, and the model is run to 2041 using SSTs that account for realistic and plausible evolutions of Pacific Ocean and Atlantic Ocean interannual to decadal variability imposed on estimates of radiatively forced SST change. The results emphasize the importance of changes in precipitation throughout the year for declines in summer soil moisture. In the worst-case scenario, a cool tropical Pacific and warm North Atlantic lead to reduced cool season precipitation and soil moisture. Drier soils then persist into summer such that evapotranspiration reduces and soil moisture partially recovers. In the best-case scenario, the opposite states of the oceans lead to increased cool season precipitation but higher evapotranspiration prevents this from increasing summer soil moisture. Across the scenarios, atmospheric humidity is primarily controlled by soil moisture: drier soils lead to reduced evapotranspiration, lower air humidity, and higher vapor pressure deficit (VPD). Radiatively forced change reduces fall precipitation via anomalous transient eddy moisture flux divergence. Fall drying causes soils to enter winter dry such that, even in the best-case scenario of cool season precipitation increase, soil moisture remains dry. Radiative forcing reduces summer precipitation aided by reduced evapotranspiration from drier soils. Significance Statement Southwest North America has long been projected to undergo aridification under rising greenhouse gases. In this model-based paper, we examine how coupling across seasons between the atmosphere and land system moves the region toward reduced summer soil moisture. The results show the dominant control on summer soil moisture by precipitation throughout the year. It also shows that even in best-case scenarios when changes in decadal modes of ocean variability lead to increases in cool season precipitation, rising spring and summer evapotranspiration means this does not translate into increased summer soil moisture. The work places projections of regional aridification on a firmer basis of understanding of the ocean driving of the atmosphere and its coupling to the land system.

  PublisherOA PDFDOI

• Estimating the Thermodynamic Contribution to Recent Greenland Ice Sheet Surface Mass Loss

  2025-10-06

  articleOpen access

  Abstract. The Greenland Ice Sheet has become the largest single frozen source of global sea level rise following a pronounced increase in meltwater runoff in recent decades. The pivotal role of anomalous anticyclonic circulation patterns in facilitating this increase has been widely documented; however, this change in atmospheric circulation has coincided with a rapidly warming Arctic. While amplified warming at high latitudes has undoubtedly contributed to trends in Greenland's mass loss, the contribution of this shift in background conditions relative to changes in regional circulation patterns has yet to be quantified. Here, we apply the pseudo-global warming method of dynamical downscaling to estimate the contribution of the change in the thermodynamic background state under global warming to observed Greenland Ice Sheet surface mass loss since the turn of the century. Our analysis demonstrates that, had the recent atmospheric dynamical forcing of the Greenland Ice Sheet occurred under a preindustrial setting, anomalous surface mass loss would have been reduced by over 62 % relative to observations. We show that the change in the thermodynamic environment under amplified Arctic warming has augmented melt of the ice sheet via longwave radiative effects accompanying an increase in atmospheric water vapor content. Furthermore, the thermodynamic contribution to surface mass loss over the exceptional melt years of 2012 and 2019 was less than half that of the long-term average, demonstrating a reduced influence during periods of strong synoptic-scale atmospheric forcing.

  PublisherOA PDFDOI

• The Puzzle Pieces of Right-sided Heart Failure: Unraveling Its Many Faces

  American Journal of Respiratory and Critical Care Medicine · 2025-05-01 · 1 citations

  articleSenior author

  Abstract The historical emphasis on the left ventricle has overshadowed the significance of the right ventricle (RV). Recent evidence highlights the poor prognosis of various cardiac conditions with comorbid RV failure. This underscores the need to address both chronic and acute insults. In patients with significant comorbidities, minimally invasive options can prevent further exacerbation of RV dysfunction. Treating reversible causes of RV failure improves morbidity and enhances overall cardiac function. We present a case of RV failure with multiple reversible causes diagnosed and treated sequentially through minimally invasive methods. A 53-year-old male with a complex cardiac history presented with persistent lower extremity edema and orthopnea unresponsive to increased Lasix. His history includes cardiac arrest, heart failure with reduced ejection fraction (EF 20-25%) due to ischemic cardiomyopathy, treated with a dual-chamber pacemaker and defibrillator, coronary artery disease with drug-eluting stents, paroxysmal atrial fibrillation on Eliquis, recurrent ventricular tachycardia post-trans-catheter ablations, hypertension, hyperlipidemia, and type 2 diabetes. On presentation he was afebrile and vitally stable. He denied any anginal symptoms. He recently recovered from a viral prodrome with URI symptoms. Physical exam revealed decreased breath sounds, S3 heart sound, elevated jugular venous pressure, hepatojugular reflux, and bilateral lower extremity pitting edema. EKG showed normal sinus rhythm with a prolonged QTc, chronic T wave inversions, and Q waves. Right Heart Catheterization revealed poor RV systolic function and concern for Atrial intracardiac shunt. Initial echocardiogram indicated a large pericardial effusion with early tamponade physiology. Subsequent pericardiocentesis and Transthoracic Echocardiogram with bubble study were suspicious for Atrial Septal Defect. Transesophageal Echocardiogram confirmed a secundum-type ASD. Staged transcatheter occlusion of ASD with an occlusion device was performed.RV dysfunction is most commonly attributed to left heart failure from ischemic disease, but other causes can contribute to progression and mortality. Other causes include right (tricuspid and pulmonary) valvular insufficiency, pulmonary embolism, AV shunts, intracardiac left-to-right shunts, ischemic heart disease, and myocarditis. Our case presents RV Failure secondary to multiple etiologies: Cardiac contusion secondary to CPR, cardiac tamponade and intra-atrial shunt. The advances in the field of Interventional Cardiology allow us to treat all these reversible causes via a minimally invasive approach in an otherwise complex patient and achieve the best outcome for the patient.

  PublisherDOI

• Supplementary material to "Estimating the Thermodynamic Contribution to Recent Greenland Ice Sheet Surface Mass Loss"

  2025-10-06

  articleOpen access
  PublisherDOI

• MeltwaterBench: Deep learning for spatiotemporal downscaling of surface meltwater

  ArXiv.org · 2025-12-13

  preprintOpen access

  The Greenland ice sheet is melting at an accelerated rate due to processes that are not fully understood and hard to measure. The distribution of surface meltwater can help understand these processes and is observable through remote sensing, but current maps of meltwater face a trade-off: They are either high-resolution in time or space, but not both. We develop a deep learning model that creates gridded surface meltwater maps at daily 100m resolution by fusing data streams from remote sensing observations and physics-based models. In particular, we spatiotemporally downscale regional climate model (RCM) outputs using synthetic aperture radar (SAR), passive microwave (PMW), and a digital elevation model (DEM) over the Helheim Glacier in Eastern Greenland from 2017-2023. Using SAR-derived meltwater as "ground truth", we show that a deep learning-based method that fuses all data streams is over 10 percentage points more accurate over our study area than existing non deep learning-based approaches that only rely on a regional climate model (83% vs. 95% Acc.) or passive microwave observations (72% vs. 95% Acc.). Alternatively, creating a gridded product through a running window calculation with SAR data underestimates extreme melt events, but also achieves notable accuracy (90%) and does not rely on deep learning. We evaluate standard deep learning methods (UNet and DeepLabv3+), and publish our spatiotemporally aligned dataset as a benchmark, MeltwaterBench, for intercomparisons with more complex data-driven downscaling methods. The code and data are available at $\href{https://github.com/blutjens/hrmelt}{github.com/blutjens/hrmelt}$.

  PublisherOA PDFDOI

• Chronic Cough, Dyspnea, and a Novel CCDC39 Variant: A Case Report of Heterotaxy Syndrome Without Cardiac Anomalies and Associated Primary Ciliary Dyskinesia

  Cureus · 2024-12-26

  articleOpen accessSenior author

  Heterotaxy syndrome is characterized by abnormal left-right arrangement of thoracoabdominal organs and is frequently associated with complex cardiac anomalies. However, cases with predominant extracardiac manifestations are increasingly recognized. This report describes a 20-year-old female of North African descent with consanguineous parentage, who presented with chronic cough and exertional dyspnea persisting over several years. Clinical examination, biochemical analyses, and vital signs were unremarkable, and there was no reported history of environmental exposures or tuberculosis. Pulmonary function testing revealed severe airway obstruction, reversible with bronchodilators. Imaging studies demonstrated a diffuse bronchiolitis pattern, an enlarged azygos vein, and polysplenia. Abdominal CT (computed tomography) revealed an interrupted inferior vena cava with azygos continuation, an enlarged left liver, a multinodular spleen, and distal pancreatic atrophy. Methicillin-resistant Staphylococcus aureus was identified in bronchoalveolar lavage, and the patient was treated with intravenous vancomycin. Further evaluations, including sinus CT, revealed bilateral frontal sinus aplasia, hypoplasia of other sinuses, and structural abnormalities such as the absence of uncinate processes. Nasal biopsy showed absent ciliary motility, and transmission electron microscopy revealed inner dynein arm defects and central apparatus abnormalities without outer dynein arm involvement. Genetic testing identified a novel homozygous c.2347_2351del (p.Phe783ThrfsTer3) PVS1 null variant in exon 17 of the CCDC39 gene, associated with autosomal recessive primary ciliary dyskinesia-14. This case highlights the overlap between heterotaxy syndrome and primary ciliary dyskinesia, suggesting that the ciliary defect contributed to both the patient’s organ laterality defects and chronic respiratory symptoms. The findings underscore the importance of a comprehensive evaluation of structural and functional abnormalities and the role of genetic testing in managing atypical presentations of heterotaxy syndrome.

  PublisherOA PDFDOI

• Understanding and Improving Greenland Ice Albedo in Climate Models

  2024-04-15

  preprintOpen access

  Meltwater production from the Greenland Ice Sheet (GrIS) is increasing rapidly, accelerating global sea level rise.However, the uncertainty of the projected sea level rise prevents proper planning of mitigations against the effects of sea level rise.This uncertainty is in large part due to a lack of understanding of the physical processes that control surface melting.Specifically, we lack understanding of the physical processes controlling ice albedo, a major driver of surface melting.Therefore, climate models often use a constant value or an overly simplified equation to model ice albedo.Consequently, ice albedo is currently not properly represented in climate models (Figure 1), with implications for surface melting and sea level rise predictions (Antwerpen et al., 2022).Here, we show how we use the available, but under-used, information from climate model output and satellite imagery to improve the representation of ice albedo.We use physics-informed machine learning (ML) tools to explore the relations between 1) the modeled atmospheric and glaciological parameters of bare ice and 2) the observed bare ice albedo.

  PublisherOA PDFDOI

• Improved treatment of snow over ice sheets in the NASA GISS climate model: towards ice sheet–climate coupling

  2024-03-08

  preprintOpen access

  Representing the interactions between ice sheets and climate is essential for more accurate prediction of climate change and sea level rise. Ice sheets interact with the overlying atmosphere via the accumulation of snow and its compaction into firn, then ice, as well as the melting of surface snow and ice and the creation of runoff water. Getting an adequate representation of heat transfer, compaction, and melting processes is essential for an accurate representation of snow on land ice in global climate models. We are implementing an improved snow model on top of land ice as part of an effort to couple the NASA GISS climate model with the PISM ice sheet model. The new snow model includes additional layers and processes that are not currently incorporated (e.g., liquid water retention, percolation and refreezing, and snow densification), and mass and energy transfer methods that are consistent with both static ice sheets (with implicit iceberg fluxes) and interactive ice sheets (with explicit dynamics). We are tuning the densification scheme of this snow model with temperature and density data from common FirnCover and SumUp observations at locations in the accumulation zone of Greenland, and we compare the resulting density profiles to other SumUp density profiles in Greenland and Antarctica. We will assess the impact of this new snow model in climate model simulations with a static ice sheet compared with the previous (simpler) 2-layer snow model. Finally, we aim to use the non-coupled simulations as a baseline to assess the impact of dynamic coupling with an interactive ice sheet model.

  PublisherDOI

• Recent Fracture-Flow Variability on Thwaites Ice Shelf and Linkages to Atmosphere-Ocean Drivers

  2024-06-10

  preprintOpen access

  The rapidly-changing Thwaites Ice Shelf is crucial for understanding ice-shelf instability and its implications for sea-level rise from Antarctica. Fractures play a significant role in this region but are poorly characterized, especially regarding their vertical depth. To address this gap, we developed a robust workflow that adapts to surface topography complexities to characterize time-varying fracture vertical properties over Thwaites using ICESat-2 altimetry measurements. We derived seasonal flow velocities from Sentinel-1 data and analyzed climate reanalysis data to examine flow-fracture interactions in the context of oceanic and atmospheric changes. The results revealed distinct fracturing and flow patterns between the eastern and western sectors of the ice shelf. Significant fracturing was observed along the shear margin and near the grounding line in the eastern sector, correlating with flow speed increases exceeding 90% at shear zones. In contrast, the western glacier tongue exhibited a less progressive fracturing pattern, with an active fracture zone downstream of the historical grounding line and overall flow deceleration. This is likely due to the stabilizing effects of grounding-zone geometry, a subglacial sill, and increased coupling to the slower-moving eastern sector. Atmospheric and oceanic reanalysis data suggest that atmosphere-sea-ice-ocean interactions could destabilize an ice shelf through shallow oceanic warming. Warm winters, reduced sea ice, and favorable winds and ocean currents can cause shoaling of warm Circumpolar Deep Water, facilitating access of warm waters to thin, structurally vulnerable areas such as shear margins and basal channels. This intensifies fracturing and triggers damage-flow-acceleration feedback that could lead to eventual ice-shelf destabilization.

  PublisherOA PDFDOI

Frequent coauthors

• Marco Tedesco

  Columbia University

  230 shared

• Cécile Agosta

  Centre National de la Recherche Scientifique

  123 shared

• Xavier Fettweis

  112 shared

• Aurélien Quiquet

  89 shared

• Christophe Dumas

  87 shared

• Nicolas C. Jourdain

  Centre National de la Recherche Scientifique

  68 shared

• Heiko Goelzer

  63 shared

• Jonathan M. Gregory

  Met Office

  57 shared