Rapid reductions and millennial-scale variability in Nordic Seas sea ice cover during abrupt glacial climate changes

Constraining the past sea ice variability in the Nordic Seas is critical for a comprehensive understanding of the abrupt Dansgaard-Oeschger (D-O) climate changes during the last glacial. Here we present unprecedentedly detailed sea ice proxy evidence from two Norwegian Sea sediment cores and an East Greenland ice core to resolve and constrain sea ice variations during four D-O events between 32 and 41 ka. Our independent sea ice records consistently reveal a millennial-scale variability and threshold response between an extensive seasonal sea ice cover in the Nordic Seas during cold stadials and reduced seasonal sea ice conditions during warmer interstadials. They document substantial and rapid sea ice reductions that may have happened within 250 y or less, concomitant with reinvigoration of deep convection in the Nordic Seas and the abrupt warming transitions in Greenland. Our empirical evidence thus underpins the cardinal role of rapid sea ice decline and related feedbacks to trigger abrupt and large-amplitude climate change of the glacial D-O events.

Sea ice is a critical component of the global climate system as it affects Earth’s albedo, phytoplankton productivity, ocean-atmosphere heat and gas exchange, and ocean circulation (1). Rapid sea ice retreat, as observed in the modern Arctic Ocean, exerts important climate feedbacks that may lead to an accelerated climate warming at northern high latitudes (2). While many climate models have difficulties in reproducing the currently observed Arctic sea ice decline (3), the rates of ongoing atmospheric warming in some Arctic regions are already comparable with those of prominent abrupt climate changes that occurred during the last glacial period (4). The latter are referred to as Dansgaard–Oeschger (D-O) climate events and known from Greenland ice core records as abrupt shifts between cold Greenland stadials (GS) and warmer Greenland interstadials (GI) occurring repeatedly ∼10–110 ka (5, 6). The millennial-scale glacial climate variability was a global phenomenon with different characteristics in the northern and southern hemispheres, but the most striking feature of the D-O events is an extremely abrupt climate transition that includes an atmospheric warming of 5–16.5 °C over the Greenland ice sheet happening in just a few decades (7). Analogous to the modern and future sea ice retreat and resulting warming in the Arctic, the abrupt D-O climate transitions are widely believed to have been amplified by rapid sea ice retreat in the Nordic Seas (8–15).Today, the Nordic Seas are largely ice-free, and warm Atlantic surface waters flow into the Norwegian Sea as far north as Svalbard at ∼80°N (Fig. 1), where the Arctic sea ice cover is being eroded, in particular in the Barents Sea. The warm Atlantic surface waters release heat to the atmosphere as it flows northward, which is accompanied by convective intermediate and deep-water formation between Norway and Greenland, feeding the lower limb of the Atlantic Meridional Overturning Circulation (AMOC) (16). A portion of the Atlantic waters continues flowing into the stratified Arctic Ocean as subsurface waters (17). While the pattern of ocean circulation during GI was fairly comparable to that today, proxy data indicate that the glacial Nordic Seas exhibited a stable surface stratification during GS, similar to the modern Arctic Ocean (13, 18). The AMOC and associated northward surface heat transport into the Nordic Seas were weakened during GS, with most extreme weakening related to Heinrich events signified by massive iceberg discharges to the North Atlantic (19, 20). Intermediate and deep waters in the stadial Nordic Seas were 2–4 °C warmer as compared with GI or modern conditions, resulting from a stable halocline and reduced open-ocean convection (21, 22). Contemporaneously, an extended sea ice cover reaching at least as far south as the Greenland–Scotland Ridge at ∼60°N insulated the high-latitude atmosphere from the deep oceanic heat reservoir (23, 24). Model simulations support a subsurface warming scenario under extended sea ice during GS (22, 25, 26) and suggest that a rapid removal of the sea ice cover might have caused the abrupt and high-amplitude D-O climate warming (11, 12, 14, 15).Open in a separate windowFig. 1.Core sites and regional context of the study area. Yellow diamonds mark the core sites investigated in this study. The map shows the core-top P_BIP₂₅ distribution (42, 43, 63), illustrating the great potential of the biomarker approach for sea ice reconstruction. Orange, yellow, and green dots mark core-top sites north, east, and south of Greenland, respectively, data of which are investigated in this study. Small black dots indicate locations of published core-top data. Purple lines mark the modern sea ice extent during September (dashed) and March (solid), averaged between A.D. 1981 and 2010 (https://nsidc.org/; ref. 64). The thin blue line shows the P_BIP₂₅ = 0.2 isoline, representing best the modern winter/spring sea ice extent. Red arrows illustrate the warm and saline North Atlantic Current (NAC). The map was produced with Ocean Data View software (65).Although there is some evidence of millennial-scale sea ice fluctuations during the last glacial, the few available sea ice proxy records (23, 24, 27–31) are mostly restricted to the southern Norwegian Sea and the Arctic Ocean, often have a limited temporal resolution, and partly reflect opposing trends regarding stadial–interstadial sea ice changes depending on the proxies used. Here we present high-resolution sea ice biomarker records from two key sites that form a North–South transect within the Atlantic inflow region in the Norwegian Sea and are thus ideally suited to record spatiotemporal shifts in sea ice cover in both the entrance and the interior of the ocean basin, oceanic fronts, and Atlantic water inflow during the last glacial (Fig. 1). Furthermore, we combine these marine sea ice proxy records with an independent sea ice record based on bromine-enrichment (Br_enr) values from an East Greenland ice core, which significantly enhances the spatial coverage, the robustness of results, and temporal constraint of the sea ice reconstruction. We focus on five representative glacial D-O cycles between 32 and 41 ka, which comprise long- and short-lasting GI as well as several GS, one of which includes Heinrich Event 4. The application of the cryptotephra-based chronological constraints provides a level of robustness as to the timing, duration, and nature of the events unfolding during abrupt climate changes. Our study provides robust empirical evidence that resolves rapid and widespread sea ice retreat in the Nordic Seas and its role in initiating and amplifying the abrupt climate change of the glacial D-O events.     

Reverse-sequencing chewing patterns evaluation in anterior versus posterior unilateral crossbite patients

It is well established that patients with a unilateral posterior crossbite exhibit reverse-sequencing chewing patterns when chewing on the affected side. The aim of the study was to compare the prevalence of reverse-sequencing chewing cycles in patients with anterior versus posterior unilateral crossbite during chewing soft and hard boluses. Eighty-six children (39 boys, 47 girls) were included in the study: 26 (10.4 ± 2.7 years) with unilateral anterior crossbite, 43 (10.2 ± 4.2 years) with unilateral posterior crossbite, and 17 (10.6 ± 2 years) with normal occlusion were selected for the study. Mandibular movements were measured with a kinesiograph (K7, Myotronics Inc. Tukwila). The kinematic signals were analyzed using custom-made software. The results showed a low prevalence of reverse-sequencing chewing cycles in patients with anterior crossbite, without any significant difference between sides and with the control group, with both soft (P = 0.33) and hard (P = 0.29) bolus. The patients with posterior unilateral crossbite showed a significant higher prevalence of reverse-sequencing chewing cycles during chewing on the crossbite side with respect to the non-crossbite side (P < 0.001) and to the control group (P < 0.001). Comparing the patients with anterior versus posterior unilateral crossbite, a significant difference (P < 0.001) in the prevalence of reverse chewing cycles was demonstrated during chewing on the posterior crossbite side only with both soft and hard bolus. In conclusion, patients with anterior versus posterior unilateral crossbite show different functional characteristics depending on which dental region is involved.     

Blood pressure circadian rhythm alterations in alpha-synucleinopathies

Journal of Neurology - We sought to analyze the blood pressure (BP) circadian rhythm in Parkinson’s disease (PD), multiple system atrophy (MSA), and pure autonomic failure (PAF) and to...     

Improvement of masticatory kinematic parameters after correction of unilateral posterior crossbite: Reasons for functional retention

Objective:To evaluate reverse-sequencing chewing cycles (RSCC) and their kinematic parameters on both sides before and after correction with the Function Generating Bite (FGB) appliance.Materials and Methods:Forty-seven patients, 8.3 ± 1.1 (mean ± SD) years of age, with unilateral posterior crossbite (35 on the right side, 12 on the left side) and 18 age-matched controls (9.1 ± 0.8 years) were selected for the study from the orthodontic division of the University of Turin, Italy. The crossbite was corrected in all patients using FGB, and mandibular motion was recorded with a kinesiograph K-7 (Myotronics, Tukwila, Wash), during chewing on both sides of a soft and a hard bolus before and after correction.Results:After correction, the percentage of RSCC significantly decreased for soft and hard (P < .001) boluses and fell within the normal range for 75% of the patients. The indices of the chewing pattern (closure angle, axis, maximum lateral excursion) significantly improved (P < .001), becoming symmetric between sides.Conclusions:The results of this study showed that the functional appliance, FGB, was able to lower the percentage of RSCC significantly, bringing them back to the normal range in 75% of cases, and to improve the kinematic parameters that become symmetric between sides.     

Differential impact of individual autonomic domains on clinical outcomes in Parkinson’s disease

Journal of Neurology - While autonomic failure is a well-known prognostic factor for more aggressive disease progression in Parkinson’s disease (PD), with a three- to sevenfold higher risk of...     

Burden of caregiving for cardiovascular dysautonomia in Parkinson’s disease

Purpose

We sought to estimate the impact of cardiovascular autonomic neuropathy (cAN) on informal caregivers of patients with Parkinson’s disease (PD), defined as individuals providing regular care to a friend, partner, or family member with PD, and to evaluate the mutual relationship between caregiver burden and patient health-related quality of life (HRQoL).

Methods

We enrolled 36 consecutive patients with PD and their informal caregivers. Patients underwent a detailed motor, autonomic, cognitive, and functional assessment. Caregivers were assessed using the Zarit Burden Interview (ZBI). Differences in caregiver burden, expressed by the ZBI score, and strength of association between caregiver burden, cAN, and HRQoL were assessed using analysis of covariance (ANCOVA), logistic regression, and linear regression analyses. Analyses were adjusted for patients’ age, PD duration, and motor and cognitive disability, as well as caregivers’ age.

Results

Moderate-severe caregiver burden was reported in 41.7% of PDcAN⁺ versus 8.7% of PDcAN⁻ (p < 0.001). The ZBI score was increased in PDcAN⁺ versus PDcAN⁻ (31.5 ± 3.4 versus 15.2 ± 2.3; p < 0.001), with tenfold higher odds (p = 0.012) of moderate-severe caregiver burden in PDcAN⁺, even after adjusting for potential confounders. The ZBI score correlated with cAN severity (p = 0.005), global autonomic impairment (p = 0.012), and HRQoL impairment (p < 0.001).

Conclusion

These results highlight the significant impact of cAN on PD caregivers and the need for targeted interventions addressing this frequently overlooked and insufficiently treated source of nonmotor disability in PD.

     

Mechanical circulatory support with the ABIOMED BVS 5000: the Toronto General Hospital experience

BACKGROUND

Acute hemodynamic collapse resulting in cardiogenic shock and impending end-organ failure is usually associated with certain death. The introduction of short-term mechanical circulatory support (MCS) devices offers potential therapy to these critically ill patients. The BVS 5000 device (ABIOMED Inc, USA) is widely used in the United States, but rarely in Canada, where device reimbursement remains a barrier.

OBJECTIVE

To present the Toronto General Hospital’s (Toronto, Ontario) initial five-year experience with this device to highlight the indications for use, common complications and overall success rates.

METHODS AND RESULTS

The institutional MCS database from 2001 to 2006 was reviewed, and 18 patients who received 30 devices in a variety of configurations were identified. The most common support configuration consisted of biventricular support (n=12), followed by isolated left ventricular support (n=4) and isolated right ventricular support in two recipients of an implantable long-term left ventricular assist device. Overall survival to device explant or transplant was 55% (n=10), of which five (50%) were successfully discharged from the hospital. The overall survival from device implant to hospital discharge was 28% (five of 18). The most common cause of death was multisystem organ failure.

CONCLUSIONS

MCS with the ABIOMED BVS 5000 can successfully resuscitate critically ill patients; however, earlier institution of this device would avoid irreversible end-organ injury, and lead to higher rates of device explant and hospital discharge. Short-term MCS devices should be available in all cardiac surgical centres in Canada to permit stabilization and evaluation of the acutely ill cardiac patient and subsequent management in a heart transplant facility.     

Machine learning applied to ambulatory blood pressure monitoring: a new tool to diagnose autonomic failure?

Journal of Neurology - Autonomic failure (AF) complicates Parkinson’s disease (PD) in one-third of cases, resulting in complex blood pressure (BP) abnormalities. While autonomic testing...     

Cardiovascular autonomic neuropathy and falls in Parkinson disease: a prospective cohort study

Journal of Neurology - Falls represent one of the main complications of Parkinson’s disease (PD), significantly lowering quality of life. Cardiovascular autonomic neuropathy (cAN) is one of...