diff --git a/packages/core/templates/partials/slide-styles.eta b/packages/core/templates/partials/slide-styles.eta
index 2d1f973..b12ea78 100644
--- a/packages/core/templates/partials/slide-styles.eta
+++ b/packages/core/templates/partials/slide-styles.eta
@@ -660,6 +660,15 @@
     animation: morkdeck-marquee-scroll 48s linear infinite;
   }
 
+  /* Pause the marquee whenever its slide is not the in-view slide.
+     The presentation toggles `.is-in-view` from the existing
+     IntersectionObserver, so overview thumbnails, off-slot slides in
+     presenter mode, and slides scrolled past in audience mode all
+     drop their compositing layer until they return to view. */
+  morkdeck-slide:not(.is-in-view) .marquee-track {
+    animation-play-state: paused;
+  }
+
   morkdeck-slide .marquee-item,
   morkdeck-slide .marquee-sep {
     font-family: var(--morkdeck-fontFamily-mono);
diff --git a/packages/wc/components/presentation/wc.ts b/packages/wc/components/presentation/wc.ts
index 949c696..35e227e 100644
--- a/packages/wc/components/presentation/wc.ts
+++ b/packages/wc/components/presentation/wc.ts
@@ -965,6 +965,15 @@ export class PresentationWC extends LitElement {
   }
 
   fireUpdates(entries: IntersectionObserverEntry[]) {
+    // Visibility-class toggle first, before any role/overview gating —
+    // this is read by the marquee CSS to pause its animation on slides
+    // that aren't currently in view (overview thumbnails, off-slot
+    // slides in presenter mode, slides scrolled out of the audience
+    // viewport). Driving it from the existing observer is essentially
+    // free; the alternative was a second IO per slide.
+    for (const entry of entries) {
+      entry.target.classList.toggle("is-in-view", entry.isIntersecting);
+    }
     // IO drives audience-mode scroll navigation only.
     if (this.role !== "audience") return;
     // Overview shows many slides at once in a grid; whichever happens